贪心，按费用排序从低到高排序，优先送费用低的，费用低的又去传递更低的。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e5+10;
ll n,p;
struct node{
	int a,b;
	int jia;
}d[N];
bool cmp(node x,node y)
{
	if(x.b==y.b)return x.a>y.a;
	return x.b<y.b;
}
ll solve()
{
	sort(d+1,d+n+1,cmp);
	ll ans=0,id=0;
	for(int i=1;i<=n;i++)
		if(d[i].jia==0)
		{
			ans+=p;
			if(id==0)id=i+1;
			
			if(d[i].b<p)
				for(int j=1;j<=d[i].a && id<=n ;j++)
					d[id++].jia=d[i].b;
		}
		else
		{
			ans+=d[i].jia;
			
			if(id==0)id=i+1;
			
			if(d[i].b<p)
				for(int j=1;j<=d[i].a && id<=n ;j++)
					d[id++].jia=d[i].b;
			
		}
			
		for(int i=1;i<=n;i++)d[i].jia=0;
	return ans;
}
int main()
{
	ios::sync_with_stdio(0);cin.tie(0);
	int t;
	cin>>t;
	while(t--)
	{
		cin>>n>>p;
		for(int i=1;i<=n;i++)cin>>d[i].a;
		for(int i=1;i<=n;i++)cin>>d[i].b;
		cout<<solve()<<"\n";
	}
	return 0;
}