L = [[-1] * 1000 for _ in range(1000)]
for i in range(1000):
    x = 0
    for j in range(1000):
        if(L[i][x % 1000] == -1):
            L[i][x % 1000] = j
        x += i

def solve(X, M):
    if(L[M%1000][X] == -1):
        return -1
    else:
        f = X * 10 ** 10
        if(f % M != 0):
            f += (M - f % M)
        # print(f)
        ans = str(f * 1000 + M * L[M % 1000][X])
        return ans

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