# https://atcoder.jp/contests/abc186/tasks/abc186_e
from math import gcd
T = int(input())
for _ in range(T):
    N, M = map(int, input().split())
    MOD = 10 ** 9


    N, S, K = MOD, M, N

    if K % MOD == 0:
        print(1 if S % MOD == 0 else -1)
        continue

    g = gcd(K, N)
    if S % g:
        print(-1)
    else:
        N //= g
        S //= g
        K //= g
        # print(N, S, K)
        # ans = -S * K^-1 (mod N)
        ans = (N - S * pow(K, -1, N)) % N
        if ans == 0:
            ans += N
        print(ans)