#include<bits/stdc++.h>
using namespace std;
int t,n,m,k,a[100005],b[100005],ans;
int main(){
  cin>>t;
  while(t--){
    cin>>n>>m,k=n;
    for(int i=1;i<=n;i++)cin>>a[i];
    for(int i=1;i<=n;i++)cin>>b[i];
    sort(b+1,b+n+1);
    for(int i=1;i<=n;i++){
      b[i]+=b[i-1];
      if(b[i]>=m){
        k=i-1;
        break;
      }
    }
    priority_queue<int>q;
    for(int i=k,j=n,pre=m;i>=1;i--){
      q.push(0);
      while(j>=1&&a[j]>b[i])q.push(pre-a[j]),pre=a[j--];
      if(a[j]<=b[i-1])ans+=q.top(),q.pop();
      else{
        int now=q.top();
        q.pop();
        if(pre-b[i]<=now)ans+=now;
        else ans+=pre-b[i],q.push(now+b[i]-a[j]),pre=a[j];
      }
    }
    cout<<ans<<'\n',ans=0;
  }
  return 0;
}