def extgcd(a, b):
    if b:
        d, y, x = extgcd(b, a % b)
        y -= (a // b) * x
        return d, x, y
    return a, 1, 0

#以下modinv
def mod_inv(a, m):
    g, x, y = extgcd(a, m)

    if g != 1:
        raise Exception()

    if x < 0:
        x += m

    return x

T=int(input())
for _ in range(T):
    N,M=map(int, input().split())
    d,x,y = extgcd(N,-10**9)
    t = 10**9 - M
    if t%d!=0:
        print(-1)
    else:
        print(x*(t//d)%(10**9))