def tle(X, M):
    for i in range(1000):
        S = str(i * M)
        if(len(S) >= len(str(X)) and S[-len(str(X)):] == str(X)):
            f = X * 10 ** 10
            if(f % M != 0):
                f += (M - f % M)
            ans = str(f * 1000 + M * i)
            assert(len(str(X)) <= len(ans) <= 18)
            assert(int(ans) % M == 0)
            assert(ans[:len(str(X))] == str(X))
            assert(ans[-len(str(X)):] == str(X))
            return ans
    return -1

T = int(input())
for _ in range(T):
    X, M = map(int, input().split())
    print(tle(X, M))