There are some easy math fuction,there are add......
You can use the add function too add,and use subtract......
There is code:
pub mod math_functions {
    pub fn add(a: i32, b: i32) -> i32 {
        a + b
    }
    pub fn subtract(a: i32, b: i32) -> i32 {
        a - b
    }
    pub fn multiply(a: i32, b: i32) -> i32 {
        a * b
    }
    pub fn divide(a: i32, b: i32) -> Result<i32, &'static str> {
        if b == 0 {
            Err("Cannot divide by zero")
        } else {
            Ok(a / b)
        }
    }
}

And use distance:
fn main(){
    let ax: i32 = ......;
    let ......
    ......
    println!("{}",distance(ax,ay,bx,by));
}