#include <bits/stdc++.h>
// #include "../cpp-dump/cpp-dump.hpp"
template<class T>
void chkmin(T &x, const T &y) {
  if (x > y) x = y;
}
template<class T>
void chkmax(T &x, const T &y) {
  if (x < y) x = y;
}
using ll = long long;

void mian() {
  int n;
  ll m, c;
  std::cin >> n >> m >> c;
  std::vector<ll> a(n), b(n);
  for (auto &x : a) std::cin >> x;
  for (auto &x : b) std::cin >> x;
  std::vector<ll> g(n);
  g[0] = m;
  for (int i = 0; i < n - 1; i++) g[i + 1] = g[i] + a[i] / c;
  // cpp_dump(g);
  ll ans = 0;
  for (int i = 0; i < n; i++) {
    g[i] -= ans;
    int l = std::min({g[i], b[i], a[i] % c});
    ans += l, g[i] -= l, b[i] -= l;
    // cpp_dump(i, l);
  }
  // cpp_dump(b, g);
  ll lim = 1e10;
  std::vector<ll> tmp(n);
  for (int i = n - 1; i >= 0; i--) {
    auto l = std::min(std::min(g[i], b[i]) / c, lim / (c + 1));
    ans += l * c, g[i] -= l * c, b[i] -= l * c, lim -= l * (c + 1), chkmin(lim, g[i]);
    for (int j = i + 1; j < n; j++) g[j] -= l * (c + 1);
    // tmp[i] = l * (c + 1);
    // cpp_dump(i, l * c, lim);
  }
  // cpp_dump(b, g);
  // std::partial_sum(tmp.begin(), tmp.end(), tmp.begin());
  // for (int i = 0; i + 1 < n; i++)
  //   g[i + 1] -= tmp[i];
  for (;;) {
    std::pair<int, int> max{0, -1};
    ll lim = 1e10;
    for (int i = n - 1; i >= 0; i--) {
      chkmax(max, {std::min({lim - 1, g[i], b[i]}), i});
      chkmin(lim, g[i]);
    }
    if (!max.first) break;
    int l = max.first, p = max.second;
    ans += l;
    g[p] -= l, b[p] -= l;
    // cpp_dump(p, l);
    for (int i = p + 1; i < n; i++)
      g[i] -= l + 1;
  }
  ans = -ans;
  for (int i = 0; i < n; i++) ans += a[i];
  std::cout << ans << '\n';
}

int main() { 
  std::cin.tie(0)->sync_with_stdio(0); 
  int t;
  std::cin >> t;
  while (t--) mian();
}