#include <iostream>

using namespace std;
typedef long long ll;
ll a[200010];
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;
        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; 
        }
        ll mx = -1;
        sum = 0;
        for(i=0;i<n;i++){
            mx = max(mx,a[i]%k);
            sum += a[i]%k;
        }
        cout << min(mx,sum/k) << "\n";
    }
}