use std::cmp::min;
use std::io;
use std::str;

fn solve(scan: &mut UnsafeScanner<io::StdinLock>) {
    let a: i64 = scan.token::<>();
    let b: i64 = scan.token::<>();
    if b % a == 0 {
        println!("0");
        return;
    }

    let mut k: i64 = 2;
    let mut ans = i64::MAX;
    loop {
        let num: i64 = b - k*a;
        let den: i64 = k-1;
        if num < den { break; }

        if num % den == 0 {
            ans = min(ans, num / den);
        }

        k += 1;
    }

    println!("{}", if ans == i64::MAX { -1 } else { ans });
}

fn main() {
    let mut scan = UnsafeScanner::new(io::stdin().lock());
    let t = scan.token::<i32>();
    for _ in 0..t {
        solve(&mut scan);
    }
}

pub struct UnsafeScanner<R> {
    reader: R,
    buf_str: Vec<u8>,
    buf_iter: str::SplitAsciiWhitespace<'static>,
}

impl<R: io::BufRead> UnsafeScanner<R> {
    pub fn new(reader: R) -> Self {
        Self {
            reader,
            buf_str: vec![],
            buf_iter: "".split_ascii_whitespace(),
        }
    }

    pub fn token<T: str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buf_iter.next() {
                return token.parse().ok().expect("Failed parse");
            }
            self.buf_str.clear();
            self.reader
                .read_until(b'\n', &mut self.buf_str)
                .expect("Failed read");
            self.buf_iter = unsafe {
                let slice = str::from_utf8_unchecked(&self.buf_str);
                std::mem::transmute(slice.split_ascii_whitespace())
            }
        }
    }
}