#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;

struct sgt {
  int n;
  std::vector<ll> tr, tg;
  void get_down(int i, ll x) { tr[i] += x, tg[i] += x; }
  void push_down(int i) {
    if (tg[i]) get_down(i << 1, tg[i]), get_down(i << 1 | 1, tg[i]), tg[i] = 0;
  }
  ll query(int i, int l, int r, int ql, int qr) {
    if (l >= ql && r <= qr) return tr[i];
    push_down(i);
    int mid = (l + r) >> 1;
    if (qr <= mid) return query(i << 1, l, mid, ql, qr);
    if (ql > mid) return query(i << 1 | 1, mid + 1, r, ql, qr);
    return std::min(query(i << 1, l, mid, ql, qr), query(i << 1 | 1, mid + 1, r, ql, qr));
  }
  void add(int i, int l, int r, int ql, int qr, ll v) {
    if (l >= ql && r <= qr) return get_down(i, v);
    push_down(i);
    int mid = (l + r)>>1;
    if (ql <= mid) add(i << 1, l, mid, ql, qr, v);
    if (qr >= mid + 1) add(i << 1 | 1, mid + 1, r, ql, qr, v);
    tr[i] = std::min(tr[i << 1], tr[i << 1 | 1]);
  }
  auto query(int l, int r) { return query(1, 0, n - 1, l, r); }
  auto add(int l, int r, ll v) { add(1, 0, n - 1, l, r, v); }
  sgt(int n) : n(n), tr(n * 4), tg(n * 4) { }
};

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;
  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;
  }
  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]);
    tmp[i] = l * (c + 1);
  }
  std::partial_sum(tmp.begin(), tmp.end(), tmp.begin());
  for (int i = 0; i + 1 < n; i++) g[i + 1] -= tmp[i];
  sgt tr(n);
  for (int i = 0; i < n; i++) tr.add(i, i, g[i]);
  std::vector<int> id(n);
  std::iota(id.begin(), id.end(), 0);
  std::sort(id.begin(), id.end(), [&](int x, int y) { return b[x] > b[y]; });
  std::priority_queue<int> pq;
  for (int i : id) {
    while (pq.size()) {
      int p = pq.top();
      ll lim = tr.query(p, p);
      if (p < n - 1) chkmin(lim, tr.query(p + 1, n - 1) - 1);
      if (lim > b[i]) {
        pq.pop();
        int l = std::min(b[p], lim);
        ans += l;
        tr.add(p, p, -l);
        tr.add(p + 1, n - 1, -l - 1);
      } else {
        break;
      }
    }
    pq.push(i);
  }
  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();
}