#include <bits/stdc++.h>
using namespace std;

const int N=1e6+5;

int a[N], b[N];

void work()
{
	int n,m,c;
	scanf("%d %d %d",&n,&m,&c);
	for(int i=1;i<=n;i++)
		scanf("%d",&a[i]);

	for(int i=1;i<=n;i++)
		scanf("%d",&b[i]);

	long long ans=m, sum=m;
	for(int i=1;i<n;i++)
	{
		sum = max(0ll,sum-a[i]%c);
		sum += a[i]/c;
		ans += a[i]/c;
	}
	sum = max(0ll,sum-a[n]);
	ans -= (sum+c)/(c+1);

	ans = -ans;
	for(int i=1;i<=n;i++)
		ans += a[i];
	printf("%lld\n",ans);
}

int main()
{
	int T;
	cin >> T;
	while(T--)
		work();
	return 0;
}