#include <bits/stdc++.h>

#define int ll
using ll = unsigned long long;

// #define MING_LE

const int mod = 998244353;
const int inf = 1e18;

using namespace std;

int a[40];
int b[40];
int c[40];
__int128_t ten[40];

void out(__int128_t x);
void solve();

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int __ = 1;
    cin >> __;

    ten[0] = 1;
    for (int i = 1; i <= 36; i++)
    {
        ten[i] = ten[i - 1] * 10;
    }

    while (__--)
        solve();

    return 0;
}

void solve()
{
    int now;
    int n, m;
    n = 0;
    cin >> now >> m;

    for (int i = 0; i <= 36; i++)
    {
        a[i] = 0;
        b[i] = 0;
    }

    while (now)
    {
        b[n] = now % 10;
        now /= 10;
        n++;
    }

    for (int i = 0; i <= 36; i++)
    {
        a[i] = 1;
        for (int j = i + 1; j <= 36; j++)
        {
            if (b[j] != 9)
                break;
            a[i]++;
        }
    }

    __int128_t ans = -1;
    for (int i = 0; i <= n; i++)
    {
        for (int j = 0; j <= 36; j++)
            c[j] = b[j];
        int p = i;
        int buffer = 0;
        __int128_t res = 0;

        while (buffer < m && p <= 36)
        {
            if (buffer + a[p] <= m && c[p] > 0)
            {
                buffer += a[p];
                int flag = 0;
                for (int j = p; j < p + a[p]; j++)
                {
                    res += (10ULL - c[j] - flag) * ten[j];
                    flag = 1;
                }
                p += a[p];
                c[p] += flag;
            }
            else
                p++;
        }

#ifdef MING_LE
        cout << i << " ";
        out(res);
        cout << " " << buffer << '\n';
        // cout << i << " " << buffer << '\n';
        // for (int i = n; i >= 0; i--)
        //     cout << c[i];
        // cout << '\n';
#endif

        if (buffer == m)
        {
            if (ans < 0)
                ans = res;
            ans = min(ans, res);
        }
    }

    if (ans < 0)
        cout << "-1\n";
    else
    {
        out(ans);
        cout << '\n';
    }
}

void out(__int128_t x)
{
    stack<int> sck;
    while (x > 0)
    {
        sck.push(x % 10);
        x /= 10;
    }
    if (sck.empty())
    {
        cout << "0";
        return;
    }
    while (!sck.empty())
    {
        cout << sck.top();
        sck.pop();
    }
}

/*
4
12345678 0
12345678 5
12345678 18
990099 5
*/

/*
1
99999999999999999 1
*/

/*
1
1000000000000000000 18
*/