Essence [Detective Suspense Novel] 'The Endless Road' Chapter One: The Missing Girlfriend

Chapter 1 (Part 1) A Small Attempt, Reaching Out, Missing Girlfriend!!
“I am Xue Zichen, a second-year student at Haioh High School in City B. My usual hobby is reading detective novels. In the future… hehe, I also hope to become a detective like Sherlock Holmes!”
In the morning, sunlight at eight o'clock shone into Zichen's bedroom. Through the window, the path of the sunlight was clearly visible. Although it was winter, having such bright sunlight was really a rare occurrence. It had snowed again last night, but the heavens are truly "understanding," knowing it's February 14th today, yet still letting the snow dance freely last night. Fortunately, the weather cleared up today.\“Ding-ling-ling”\Zichen's phone rang. He was the only one in the house. His parents had gone abroad for work. They once suggested he study overseas, but he stubbornly refused, insisting on completing his education in the country.\“…Hello…” Stretching an arm out from under the covers, he fumbled around on the table beside him for a while before answering the call. On the other end came an urgent voice, and Zichen quickly sat up in bed. It was the intermittent sound of a girl crying, “Wuu… Zichen… my… my sister-in-law… she… wuu…” It was his classmate Xia Yue'er. Zichen didn't know how heartbroken she was crying on the other end of the phone.
Zichen comforted Yue'er to calm her down and asked, “Yue'er, what's wrong? Why are you crying so hard? What happened to your sister-in-law?”
She was still sobbing on the phone. After a few moments, Yue'er spoke, “Zichen, you have to come quickly! My sister-in-law… my sister-in-law hasn't come back since she went out this morning, and… we also received a letter…” Zichen's heart twitched, thinking, “Hmm… a kidnapping?” “Alright, I'll come right away!”
A few minutes later, Zichen arrived at Yue'er's brother's house. Since it happened suddenly, the disappearance of Yue'er's sister-in-law was known only to a few of them. The police and family hadn't been informed yet.
In the living room, Yue'er's brother leaned on his hands with his head down, his hair messy, looking extremely anxious. Yue'er welcomed Zichen in and brought him to her brother. Sitting opposite her brother Xia Tian, she seemed to see a glimmer of hope and said, “Brother, this is Xue Zichen, the detective I often tell you about. He's from our school! Maybe he can help us!”"Zi Chen, feeling a bit embarrassed, quickly explained, 'Hehe, it's not like that; I just like reading detective novels.' \ Xia Tian didn't look up at Zi Chen, only muttered softly, 'Tch… just a high school student, playing detective games!!' \ Yue'er glanced at her brother and said, 'Hehe, it's okay, Zi Chen! Brother is just too anxious. Let me give you the letter first.' Yue'er handed the letter on the table to Zi Chen, who was taken aback when he saw it because there were traces of blood on it. The letter's contents were as follows:
'Your girlfriend is in my hands, location: next to the fountain in Love River Park. Regarding the amount of money for the ransom, choose from the following four groups: \||×1224832\13471123\15413\1111111 \ Hehe, the time is 11 a.m. today! If the deadline passes, you know the consequences! — Location code 90000-5'
Examining the letter, the blood was shaped like a heart, which puzzled Yue'er and Xia Tian and was also the reason they temporarily did not notify the family or the police. The heart shape surrounded the four lines of numbers. This was the suspicious part, and not just that—Zi Chen analyzed it for Yue'er: 'If this were a kidnapping, why would there be a heart shape? Completely unnecessary, just to prove the kidnapper likes hearts, and… this isn't even blood!' Yue'er and Xia Tian felt a surge of alertness at this remark, and Xia Tian came closer, seeming to see hope. Zi Chen continued, 'Not only that, look at the ransom he's asking for! The amount is large, not to mention it's so scattered. Also, the first line of numbers starts with '×'? I don't know if this means multiply or cross!' \ At this, Zi Chen suddenly understood, muttering to himself, 'Cross? Multiply?' He picked up the letter again to examine it, and a few seconds later, he laughed at the letter, 'Xia Tian, change your clothes! Hmm~ Your wife is going to get anxious!' Yue'er and Xia Tian looked at him puzzled, 'Your wife usually likes detective stories or puzzle number games too, right?' Xia Tian confidently answered for Zi Chen. 'Hehe, just as I thought!' Zi Chen said with confidence. 'Exactly. Actually, this letter is a puzzle, and your wife's current location is also in it! The location code can be understood only by analyzing the entire letter. If you read the '-' before the location code 5 as a negative, meaning subtract in reverse, it can also be interpreted as 'arrive'! Hehe, your wife's location is now clearly visible!'So, big brother, go change your clothes~"
So, does what Zichen said make sense? Hehe, the answer will be revealed in Chapter 1 (Part 2). Friends who like detective novels and puzzle games, let's have a warm-up first. Leave your answers, the meaning of the four-digit number, and the location. Reply with your answers~ Hehe, your support is the motivation for me to keep writing!