use proconio::input;

fn main() {
    input! {
        t: usize,
        ab: [(usize, usize); t],
    }

    for &(a, b) in &ab {
        match solve(a, b) {
            Some(min_x) => println!("{}", min_x),
            None => println!("-1"),
        }
    }
}

fn solve(a: usize, b: usize) -> Option<usize> {
    if a == b {
        return Some(0);
    }

    for k in (2..=b / a).rev() {
        if (b - a * k) % (k - 1) == 0 {
            return Some((b - a * k) / (k - 1));
        }
    }

    None
}