#include <bits/stdc++.h>

using namespace std;
/*
kai_sort(vector <int> nums) {
    if (nums.size <= 1) {
        return nums;
    }
    int pivot = nums[0];
    vector <int> less;
    vector <int> more;
    count++;
    for (i = 1; i < nums.size; ++i) {
    	// Comparison
        if (nums[i] < pivot) {
            less.append(nums[i]);
        }
        else {
            more.append(nums[i]);
        }
    }
    vector <int> sorted_less = kai_sort(less);
    vector <int> sorted_more = kai_sort(more);
    vector <int> ans = sorted_less + pivot + sorted_more;
    
    return ans;
}
*/

vector <int> populateArray(vector <int> array, int size){
    for(int num = 1; size > 0; size--, num++){
        array.push_back(num);
    }
    return array;
}

int maxComp(int num){
    int count = 0;
    while(num > 0){
        num = num + (num - 1);
    }
    return num;
}

vector <int> scatterArray(vector <int> array, int & c){
    int count = 0;
    while(count < c){
        int index = array.size()-1;
        int prev = array.size()-2;
        while(index >= 1){
            array.swap(array[index], array[prev]);
            index--;
            prev--;
            count++;
        }
    }
    return array;
}

int main(){
    int q;
    cin >> q;
    for(int a0 = 0; a0 < q; a0++){
        int len;
        int c;
        cin >> len >> c;
        int max = maxComp(len - 1);
        if(max < c){
            cout << -1 << endl;
            continue;
        }
        vector <int> array(len);
        populateArray(array, len);
        scatterArray(array, c);
        for(int i = 0; i < array.size(); i++){
            cout << array[i];
        }
    }
    return 0;
}