#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
main()
{
ll t, x, y, k, p, f, j,m;
cin >> t;
for (int i = 0; i <= t; i++)
{
cin >> x >> y;
k = x;
p = 10;
f = 1;
if (x % y == 0)
{
cout << x;
}
else
{
while (f == 1)
{
k = x * p;
if (k % y == 0)
{
if (k > 1000000000000000000)
{
cout << (-1);
}
else
{
cout << k;
f = 0;
}
}
j = k % y;
m = y - j;
if (m < p)
{
if (f == 1)
{
if (k + m > 1000000000000000000)
{
cout << -1;
}
else
{
cout << k + m;
f = 0;
}
}
}
p = p * 10;
}
}
}
}