import sys
import math
import bisect
from heapq import heapify, heappop, heappush
from collections import deque, defaultdict, Counter
from functools import lru_cache
from itertools import accumulate, combinations, permutations, product

sys.set_int_max_str_digits(10 ** 6)
sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
MOD99 = 998244353

input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()
SMI = lambda: input().split()
SLI = lambda: list(SMI())
EI = lambda m: [NLI() for _ in range(m)]


def main():
    T = NI()
    for _ in range(T):
        N, M = NMI()
        P = 10**9
        g = math.gcd(N, P)
        if M % g:
            print(-1)
        else:
            N //= g
            M //= g
            P //= g
            x = -M * pow(N, -1, P) % P
            if x == 0:
                x = P
            print(x)


if __name__ == "__main__":
    main()