#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using mint = atcoder::static_modint<998244353>;
// using mint = atcoder::static_modint<1000000007>;
using ld = long double;
using ll = long long;
#define mp(a,b) make_pair(a,b)
#define rep(i,s,n) for(int i=s; i<(int)n; i++)
const vector<int> dx{1,0,-1,0},dy{0,1,0,-1};

void solve(){
    int n,k;cin >> n >> k;
    vector<ll> a(n);rep(i,0,n)cin >> a[i];
    ll sum=0;
    rep(i,0,n)sum+=a[i];
    sum%=k;
    if(sum!=0){
        cout << -1 << "\n";
        return;
    }
    ll s=0;
    ll need=0;
    rep(i,0,n){
        s=max(s,a[i]%k);
        need+=a[i]%k;
    }
    need/=k;
    cout << min(s,need) << "\n";
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T;cin >> T;
    while(T--)solve();
}