#include <bits/stdc++.h>
using namespace std;
using ll=long long;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}

void solve();
// CITRUS CURIO CITY / FREDERIC
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    ll N, K;
    cin >> N >> K;
    vector<ll> A(N);
    rep(i, 0, N) cin >> A[i];
    if (vec_sum(A) % K){
        cout << "-1\n";
        return;
    }
    ll st = 0;
    for (auto x : A) chmax(st, x % K);
    ll ans = ILL;
    So(A);
    auto g = [&](ll a) -> vector<ll> {
        // diff が a 以下のものを全て消す
        vector<ll> res(N);
        rep(i, 0, N){
            if (A[i] >= a){
                res[i] = ((A[i] - a + K - 1) / K) * K;
            }
            res[i] = A[i] - res[i];
        }
        return res;
    };
    auto f = [&](int ind) -> void {
        auto B = g(st);
        ll sum = vec_sum(B);
        ll mx = vec_max(B);
        if (mx <= sum / K){
            chmin(ans, sum);
            return;
        }
        vector<int> order;
        ll cyc = (A[ind] - B[ind]) / K;
        rep(i, ind, N) order.push_back(i);
        stable_sort(all(order), [&](int l, int r){
            return B[l] < B[r];
        });
        for (auto id : order){
            if (id == ind) cyc--;
            if (cyc < 0) break;
            sum += K;
            chmax(mx, B[id] + K);
            // a = 0, 1, ... , cyc - 1 であって、
            // (mx + a * K) * K <= (sum + a * K * (N - ind))
            // を満たす最小の a
            ll tmp1 = mx * K - sum;
            ll tmp2 = K * (N - ind - K);
            if (tmp1 <= 0){
                chmin(ans, sum);
            }
            else if (tmp2 > 0){
                ll a = (tmp1 + tmp2 - 1) / tmp2;
                if (a <= cyc) chmin(ans, sum + a * K * (N - ind));
            }
        }
    };
    rep(i, 0, N){
        f(i);
        chmax(st, A[i]);
    }
    if (ans == ILL) cout << "-1\n";
    else{
        cout << ans / K << "\n";
    }
}