#include <stdio.h>
#include <bits/stdc++.h>
//%lld
typedef long long ll;
#define si(a) scanf("%d", &a)
#define sii(a, b) scanf("%d%d", &a, &b)
#define pi(a) printf("%d\n", a)

using namespace std;
ll vetor[10000000];

int main(){
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    int t, d, k;
    int e;
    cin>>t;
    while(t--){
        int p = 0;
        int temp = 0;
        ll saida = 0;
        cin>>e;
        for(int i = 0;i<=e;i++)cin>>vetor[i];
        cin>>d>>k;
        for(int i = 0;;i++){
            p+=d;
            temp+=p;
            if(temp>=k){
                for(int j = 0;j<=k;j++){
                    saida+=vetor[j]*pow(i, j);
                }
                break;
            }
        }
        cout<<saida<<endl;
    }
}