#include <algorithm>
#include <iostream>
using namespace std;
typedef long long ll;
typedef pair<ll, int> P;

const ll INF = 8000000000000000000;

void solve()
{
    int n, k;
    cin >> n >> k;
    ll a[2005];
    ll s = 0;
    for (int i = 0; i < n; i++)
    {
        cin >> a[i];
        s += a[i] % k;
    }
    if (n == k)
    {
        for (int i = 0; i < n - 1; i++)
        {
            if (a[i] % k != a[i + 1] % k)
            {
                cout << -1 << endl;
                return;
            }
        }
        cout << a[0] % k << endl;
        return;
    }
    if (s % k)
    {
        cout << -1 << endl;
        return;
    }
    sort(a, a + n, greater<ll>());
    ll x = 0;
    ll h = 0;
    ll ans = INF;
    for (int r = n; r > k; r--)
    {
        P p[4005];
        ll s = x;
        for (int i = 0; i < r; i++)
        {
            p[i] = P(a[i] % k + (h / k) * k, i);
            if (p[i].first < h)
            {
                p[i].first += k;
            }
            s += p[i].first;
        }
        sort(p, p + r);
        int j;
        for (j = 0; j < r; j++)
        {
            if (p[j].second == r - 1)
            {
                break;
            }
        }
        for (int i = r; i < r * 2; i++)
        {
            p[i] = P(p[i - r].first + k, p[i - r].second);
        }
        bool g = false;
        for (int e = 0; e < r; e++)
        {
            ll y = (p[e + r - 1].first * k - s) / ((r - k) * k);
            if (y * ((r - k) * k) < p[e + r - 1].first * k - s)
            {
                y++;
            }
            if (y < 0)
            {
                continue;
            }
            bool f = true;
            if (j >= e && p[j].first + y * k > a[p[j].second])
            {
                f = false;
            }
            if (j < e && p[j].first + k + y * k > a[p[j].second])
            {
                f = false;
            }
            if (f)
            {
                g = true;
                ans = min(ans, (s + y * k * r) / k);
            }
            s += k;
        }
        x += a[r - 1];
        h = a[r - 1];
    }
    cout << (ans < INF ? ans : -1) << endl;
}

int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        solve();
    }
}