#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define vi vector<int>
#define vl vector<ll>
#define vii vector<pair<int,int>>
#define vll vector<pair<ll,ll>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>
#define vvii vector<vector<pair<int,int>>>
#define vvll vector<vector<pair<ll,ll>>>
#define vst vector<string>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define mkunique(x) sort(all(x));(x).erase(unique(all(x)),(x).end())
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005;
const ll INF=15LL<<58;

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int Q;cin>>Q;
    while(Q--){
        ll N,K;cin>>N>>K;
        vl X(N);
        ll sum=0;
        for(int i=0;i<N;i++){
            cin>>X[i];
            sum+=X[i]%K;
        }
        if(sum%K){
            cout<<-1<<"\n";
            continue;
        }
        sort(all(X),[&](ll a,ll b){
            if(a%K==b%K) return a<b;
            else return a%K<b%K;
        });
        ll T=sum/K;
        vl Y(N);
        ll ma=0;
        for(int i=0;i<N;i++){
            Y[i]=X[i]%K;
            chmax(ma,Y[i]);
        }
        if(ma<=T){
            cout<<T<<"\n";
            continue;
        }
        ll ans=INF;
        for(int q=0;q<3*N;q++){
            for(int i=0;i<N;i++){
                if(Y[i]<X[i]){
                    Y[i]+=K;
                    T++;
                    chmax(ma,Y[i]);
                    if(ma<=T) chmin(ans,T);
                }
            }
        }
        if(ans==INF) ans=-1;
        cout<<ans<<"\n";
    }
    
}