def solve(A: int, B: int):
    for x in range(10**5):
        if (B + x) % (A + x) == 0:
            return x
    for n in range(10**5, 1, -1):
        if B - n * A < 0:
            continue
        if (B - n * A) % (n - 1) == 0:
            return (B - n * A) // (n - 1)
    return -1


T = int(input())
for _ in range(T):
    print(solve(*map(int, input().split())))