#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

void solve() {
  int n, k; cin >> n >> k;
  vector<ll> a(n);
  for (ll& a_i : a) cin >> a_i;
  priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> que;
  ll op = 0, must = 0;
  REP(i, n) {
    const ll rem = a[i] % k;
    op += rem;
    chmax(must, rem);
    if (rem < a[i]) que.emplace(rem, i);
  }
  if (op % k != 0) {
    cout << "-1\n";
    return;
  }
  op /= k;
  const int threshold = max(n * n * 10, 10000); // 未証明のためTLE対策
  for (int counter = 0; op < must; ++counter) {
    if (que.empty() || counter >= threshold) {
      cout << "-1\n";
      return;
    }
    const auto [rem, i] = que.top(); que.pop();
    ++op;
    chmax(must, rem + k);
    if (rem + k * 2 <= a[i]) que.emplace(rem + k, i);
  }
  cout << op << '\n';
}

int main() {
  int t; cin >> t;
  while (t--) solve();
  return 0;
}