/**
	author:  shobonvip
	created: 2025.03.08 00:37:22
**/

#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;
}

struct S {
	ll sum, max, maxind;
};

S op(S a, S b) {
	return S{a.sum + b.sum, max(a.max, b.max), a.max >= b.max ? a.maxind : b.maxind};
}

S e() {
	return S{0, -(ll)1e18, -1};
}

void solve() {
	ll n, k; cin >> n >> k;

	vector<ll> a(n);
	rep(i,0,n) {
		cin >> a[i];
	}

	if(sum(a)%k!=0){
		cout<<-1<<'\n';
		return;
	}
	bool mode=1;
	rep(i,0,n){
		if(a[i]%k!=0)mode=0;
	}
	if(mode){
		cout<<0<<'\n';
		return;
	}

	vector<S> init(n);
	rep(i,0,n){
		if(a[i]>k*(k-1)/2){
			ll tar = 1 + (a[i]-k*(k-1)/2-1)/k;
			a[i] -= tar*k;
		}
		init[i] = S{a[i], a[i], i};
	}
	

	segtree<S,op,e> seg(init);

	ll ans = 9e18;
	while(true){
		S r = seg.all_prod();
		//cout<<r.max<<' '<<k<<' '<<r.sum<<endl;
		if(r.max*k<=r.sum) ans=r.sum/k;
		if(r.max<k) break;
		ll i = r.maxind;
		a[i]-=k;
		seg.set(i,S{a[i],a[i],i});
	}

	if (ans >= 8e18){
		cout<<-1<<'\n';
	}else{
		cout<<ans<<'\n';
	}






}

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