#include <bits/stdc++.h>

using namespace std;

template<class F, class S>
ostream &operator<<(ostream &s, const pair<F, S> &v) {
    s << "(" << v.first << ", " << v.second << ")";
    return s;
}
template<ranges::range T> requires (!is_convertible_v<T, string_view>)
istream &operator>>(istream &s, T &&v) { 
    for (auto &&x : v) s >> x; 
    return s; 
}
template<ranges::range T> requires (!is_convertible_v<T, string_view>)
ostream &operator<<(ostream &s, T &&v) { 
    for (auto &&x : v) s << x << ' '; 
    return s; 
}

#ifdef LOCAL
template<class... T> void dbg(T... x) {
    char e{};
    ((cerr << e << x, e = ' '), ...);
}
#define debug(x...) dbg(#x, '=', x, '\n')
#else
#define debug(...) ((void)0)
#endif

#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define ff first
#define ss second

template<class T> inline constexpr T inf = numeric_limits<T>::max() / 2;
bool chmin(auto &a, auto b) { return (b < a and (a = b, true)); }
bool chmax(auto &a, auto b) { return (a < b and (a = b, true)); }

using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128;
using u128 = unsigned __int128;

constexpr i64 mod = 998244353;

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

    vector<i64> A(n);
    cin >> A;

    const i64 sum = reduce(all(A), 0LL);
    if (sum % k != 0) {
        cout << -1 << '\n';
        return;
    }

    auto check1 = [&](i64 t) -> bool {
        i64 rem = t * k;
        i64 s = 0;
        for (i64 x : A) {
            if (x % k > t) {
                return false;
            }
            rem -= x % k;
            s += min((t - x % k) / k, x / k);
        }
        if (rem < 0 or rem > s * k) {
            return false;
        }
        return true;
    };

    auto check2 = [&](i64 t) -> bool {
        i64 rem = t * k;
        i64 s = 0;
        for (i64 x : A) {
            if (x % k > t) {
                return false;
            }
            rem -= x % k;
            s += (t - x % k) / k;
        }
        if (rem < 0 or rem > s * k) {
            return false;
        }
        return true;
    };

    const i64 upper = sum / k;
    i64 ans = inf<i64>;
    for (i64 r = 0; r < k; r++) {
        i64 p = *ranges::partition_point(
            views::iota(0, upper / k + 1), 
            [&](i64 x) {
                return !check2(r + x * k);
            }
        );
        if (check1(r + p * k)) {
            chmin(ans, r + p * k);
        }
    }

    if (ans == inf<i64>) {
        ans = -1;
    }
    cout << ans << '\n';
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);

    int t = 1;
    cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}