#include <iostream>
#include <vector>

using namespace std;

int find_minN(int M, int N, int &flag, int &N_chg)
{
    int idx = 1;
    int tmp = M;
    while(tmp >= 10)
    {
        tmp = tmp / 10;
        ++idx;
    }

    // 不够M的位
    if(N < idx)
        return -1;
    else if(N == idx)
        return M;
    
	int minsa = 1;
    for(int i = 0; i < idx; ++i)
    {
        minsa *= 10;
    }
    int other = minsa % M;
    if(other == 0)
    {
        N_chg = N - idx - 1;
        flag = true;
        return minsa;
    }
    else
    {
        flag = true;
        N_chg = N - idx - 1;
        return (minsa / M + 1) * M;
    }
}

int main()
{
    int times = 0;
    cin >> times;
    vector<vector<int>> input(times, vector<int>(2, 0));
    for(int i = 0; i < times; ++i)
    {
    	cin >> input[i][0] >> input[i][1];
	}
    
    
    for(int i = 0; i < times; ++i)
    {
        int flag = false;
        int newN = 0;
        int res = find_minN(input[i][1], input[i][0], flag, newN);
        if(!flag)
            cout << res << endl;
        else
        {
            cout << res;
            for(int j = 0; j < newN; ++j)
                cout << 0;
            if(i != times - 1)
				cout << endl;
        }
    }
}