#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
typedef long long ll;
ll inf = 1000000000000000;
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t; cin >> t;
    while(t){
        t--;
        ll i,n,k; cin >> n >> k;
        vector<ll> a(n);
        for(i=0;i<n;i++) cin >> a[i];
        ll sum = 0;
        for(i=0;i<n;i++) sum += a[i];
        if(sum%k!=0){
            cout << -1 << "\n";
            continue; 
        }
        vector<pair<ll,ll>> b(n);
        for(i=0;i<n;i++) b[i] = {a[i]%k,i};
        sort(b.begin(),b.end());
        vector<ll> _a(n),c(n);
        for(i=0;i<n;i++){
            _a[i] = a[b[i].second];
            c[i] = b[i].first;
        }
        for(i=0;i<n;i++) a[i] = _a[i];
        ll mx = -1;
        sum = 0;
        for(i=0;i<n;i++){
            mx = max(mx,c[i]); sum += c[i];
        }
        if(k*mx<=sum){
            cout << sum/k << "\n";
            continue;
        }
        int j = 0;
        ll ans = inf;
        for(i=0;i<2*n*k;i++){
            if(c[i] + k<=a[i]){
                c[i] += k;
                mx = max(mx,c[i]);
                sum += k;
            }
            j++;
            if(j==n) j = 0;
            if(k*mx<=sum){
                ans = sum/k;
                break;
            }
        }
        if(ans==inf) cout << -1 << "\n";
        else cout << ans << "\n";
    }
}