#include<bits/stdc++.h>
using namespace std ;
#define faster() ios::sync_with_stdio(false); cin.tie(nullptr) ; cout.tie(nullptr);
#define endl "\n"
#define int long long
const int MOD = 1e9 + 7 ;
 
void solve(){
    int n , x ; cin >> n >> x ;
    vector<int> a(n);
    for(int i = 0 ; i < n ; i++) cin >> a[i];
    int ans = a[0];
    for (int i = 1; i < n; i++){
        ans = (ans * x + a[i]);
        ans %= MOD ;
    }       
    cout << ans << endl;
}
 
signed main(){
    faster();
    int test ;
    cin >> test;
    while(test--)   solve();
}

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