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

#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 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;
		}
		if (p*k<=cost) return true;
		return false;

	};

	for(ll i=0;i<=min(sum(c),k);i++) {
		if (check(i)) {
			cout << i + s/k << '\n';
			return;
		}
	}

	ll bsum = sum(b);
	vector<segtree<ll,op,e>> seg1(k, segtree<ll,op,e>(k+1));
	vector<segtree<ll,op,e>> seg2(k, segtree<ll,op,e>(k+1));
	vector<bool> seen(k);

	ll tmp;
	auto f = [&](ll x) -> bool {
		return x <= tmp;
	};
	
	vector ri(k, vector<pair<ll,ll>>(n));
	vector<ll> piv(k);

	for (ll i=k; i<=min(sum(c),n*k+10); i++) {
		ll p = i+s/k;
		int var=p%k;
		if (!seen[var]){
			rep(x,0,n){
				ri[var][x] = pair(c[x]-(p-b[x])/k, (p-b[x])%k);
				seg1[var].set(k, seg1[var].get(k) + min(c[x],(p-b[x])/k));
				seg2[var].set(k, seg2[var].get(k) + min(c[x],(p-b[x])/k) * k);
				// not c[x] <= (p-b[x])/k
				// <=> c[x] - (p-b[x])/k > 0
				if (c[x]*k+b[x] > p) {
					ll am = (p-b[x])%k;
					seg1[var].set(am, seg1[var].get(am) + 1);
					seg2[var].set(am, seg2[var].get(am) + am);
				}
			}
			sort(all(ri[var]));
			while(piv[var]<n && ri[var][piv[var]].first <= i/k-1) piv[var]++;
			seen[var] = 1;
		}else{
			seg1[var].set(k, seg1[var].get(k) + (n - piv[var]));
			seg2[var].set(k, seg2[var].get(k) + (n - piv[var]) * k);
			// now ... c[i] - (p-b[i])/k >= 0

			while(piv[var]<n && ri[var][piv[var]].first <= i/k-1) {
				ll am = ri[var][piv[var]].second;
				seg1[var].set(am, seg1[var].get(am) - 1);
				seg2[var].set(am, seg2[var].get(am) - am);
				piv[var]++; 
			}
			// now ... c[i] - (p-b[i])/k >= 1
		}

		tmp = i;
		ll cost = bsum;
		ll v = seg1[var].min_left(k+1, f);
		tmp -= seg1[var].prod(v, k+1);
		cost += seg2[var].prod(v, k+1);
		assert(tmp >= 0);
		if (v-1 >= 0){
			cost += (v-1) * tmp;
		}

		if (p*k<=cost) {
			cout << p << '\n';
			return;
		}

	} 

	cout << -1 << '\n';
	return;

	

}

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