def main():
    t = int(input())
    for _ in range(t):
        n, m = map(int, input().split())
        cntn1 = cntn2 = cntm1 = cntm2 = 0
        x = n
        while x%2==0:
            x //= 2
            cntn1 += 1
        while x%5==0:
            x //= 5
            cntn2 += 1
        x = m
        while x%2==0:
            cntm1 += 1
            x //= 2
        while x%5==0:
            x //= 5
            cntm2 += 1
        if min(cntn1, 9) > cntm1 or min(cntn2, 9) > cntm2:
            print("-1")
            continue
        div = (1<<min(cntn1, 9))*pow(5, min(cntn2, 9))
        x = n//div
        y = m//div
        modulo = 1000000000//div
        inv = pow(x, -1, modulo)
        res = (modulo-y*inv%modulo)%modulo
        print(res if res else modulo)


if __name__ == "__main__":
    main()