#include <bits/stdc++.h>
using namespace std;
#define int long long
void solve() {
  int n, m, c; cin >> n >> m >> c;
  int a[n];
  for(int i=0;i<n;i++) cin>>a[i];
  for(int i=0;i<n;i++) cin>>a[i];
  int v[n], g[n];
  for(int i=0;i<n;i++) v[i]=(a[i]%c), g[i]=(a[i]/c);
  int cst = 0, s = 0;
  for(int i=n;i--;) {
    g[i]=min(s,a[i]/c);
    v[i]=a[i]-c*g[i];
    cst += c*g[i];
    s += v[i] - g[i];
  }
  if(m<=s) cout<<cst+s-m<<"\n";
  else cout<<max(0LL,cst+s-m+(m-s-1)/(c+1)+1)<<"\n";
}
main() {
  int t; cin >> t;
  while(t--) solve();
}