/**
	author:  shobonvip
	created: 2025.03.07 22:05:11
**/

#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
using namespace std;

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)
#define all(v) v.begin(), v.end()

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

ll op(ll a,ll b) {
	return a + b;
}
ll e(){
	return 0;
}

void solve() {
	ll k, n;
	cin >> n >> k;
	vector<ll> a(n);
	vector<ll> b(n);
	vector<ll> c(n);
	ll s = 0;
	rep(i,0,n) {
		cin >> a[i];
		b[i] = a[i] - a[i] / k * k;
		c[i] = a[i] / k;
		s += b[i];
	}

	vector<ll> d = c;
	sort(all(d));


	if (s % k != 0) {
		cout << -1 << '\n';
		return;
	}

	if (s == 0) {
		cout << 0 << '\n';
		return;
	}

	auto check = [&](ll i) -> ll {
		ll p = i + s/k;
		ll freedom = 0;
		ll cost = 0;
		vector<ll> amari(k);
		rep(i,0,n) {
			if (b[i] > p) {
				cost += p;
			}else {
				freedom += min(c[i], (p - b[i]) / k);
				if (a[i] > p) {
					amari[(p - b[i]) % k] += 1;
				}
				cost += b[i];
			}
		}
		ll left = i;
		{
			ll targ = min(freedom, left);
			freedom -= targ;
			left -= targ;
			cost += targ * k;
		}
		rrep(i,0,k) { 
			ll targ = min(amari[i], left);
			left -= targ;
			amari[i] -= targ;
			cost += targ * i;
		}
		return p*k-cost;

	};

	ll ub=sum(c);
	ll lb=0;
	while(ub-lb>2){
		ll t1=(ub*2+lb)/3;
		ll t2=(ub+lb*2)/3;
		if(check(t1)<=check(t2)){
			lb=t2;
		}else{
			ub=t1;
		}
	}


	bool mode=0;
	ll ind=-1;
	for(ll i=lb;i<=ub;i++){
		if(check(i)<=0){
			mode=1;
			ind=i;
			break;
		}
	}

	if(!mode){
		cout<<-1<<'\n';
		return;
	}


	ll lb2=-1;
	ll ub2=ind;
	while(ub2-lb2>1){
		ll t=(ub2+lb2)/2;
		if(check(t)<=0)ub2=t;
		else lb2=t;
	}
	cout<<ub2+s/k<<endl;

}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	int t; cin >> t;
	while(t--) solve();
}