#include<bits/stdc++.h>
using namespace std;
#define int long long
#define INF 0x3f3f3f3f3f3f3f3f
#define pii pair<int,int>
#define fi first
#define se second
#define all(_a) _a.begin(), _a.end()

void solve(){
    int n,m;
    cin>>n>>m;
    vector<int>a;
    vector<int>b(n+1);
    for(int i=1;i<=n;i++)cin>>b[i];

    for(int i=1;i<=n;i++){
        int x;
        cin>>x;
        a.push_back(x);
    }
    
    sort(all(a));
    for(int i=1;i<n;i++)a[i]+=a[i-1];
    priority_queue<int>q;
    int res=0;
    for(int i=n;i>=1;i--){
        int cnt=0;
        int mi=m;
        while(a.size()&&a.back()>=b[i]){
            cnt++;
            mi=min(mi,a.back());
            a.pop_back();
        }
        //cout<<cnt<<endl;
        if(cnt==0){
            if(i==n)q.push(m-b[i]);
            else q.push(m-b[i]);
            m=b[i];
            continue;
        }
        while(cnt>=2&&q.size()){
            cnt--;
            res+=q.top();
            q.pop();
        }
        if(q.size()==0){
            res+=m-mi;
            q.push(mi-b[i]);
            m=b[i];
         
        }else{
            if(m-mi>q.top()){
                res+=m-mi;

                auto t=q.top();
                q.pop();
                t+=mi-b[i];
                q.push(t);

                m=b[i];
            }else{
                res+=q.top();
                q.pop();
                q.push(m-b[i]);
                m=b[i];
            }
        }
        //cout<<res<<endl;

    }
   cout<<res<<endl;

}
signed main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr), cout.tie(nullptr);
    cout << setiosflags(ios::fixed) << setprecision(15);
    int T;
    T=1;
    cin>>T;
    while(T--)solve();
    return 0;
}