//xhz.cpp
#include<bits/stdc++.h>
using namespace std;
int n,m,c,a[1000003],b[1000003];
void solve(){
	cin>>n>>m>>c;
	for(int i=0;i<n;i++)cin>>a[i];
	for(int i=0;i<n;i++)cin>>b[i];
	map<int,long long>mp;
	mp[0]=m;
	long long ans=0;
	for(int i=0;i<n;i++){
		int tmp=b[i];
		while(mp.size()){
			auto it=mp.begin();
			if((it->first+1)*(it->second)<=b[i]){
				ans+=it->first*it->second;
				b[i]-=(it->first+1)*(it->second);
				mp.erase(it);
			}else{
				int t=it->first;
				it->second-=b[i]/(t+1)+1;
				ans+=b[i]/(t+1)*t;
				b[i]%=(t+1);
				int f=c-(a[i]-tmp+b[i])%c;
				if(c-f-b[i]<=0){
					ans+=c-f;
					b[i]-=c-f;
					mp[t+f-c]++;
				}else if(t-b[i]<=f||b[i]+f>tmp){
					ans+=b[i];
					mp[t-b[i]]++;b[i]=0;
				}else mp[t]++;
				if(!it->second)mp.erase(t);
				break;
			}
		}tmp-=b[i];
		tmp=a[i]-tmp;
		ans+=tmp;
		mp[0]+=tmp/c;
		if(tmp%c!=0&&(tmp/c+1)*c<=a[i]){
			mp[(tmp/c+1)*c-tmp]++;
			tmp=(tmp/c+1)*c;
		}mp[c]+=(a[i]-tmp)/c;
	}
	cout<<ans<<'\n';
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int T;cin>>T;
	while(T--)solve();
}