#include<bits/stdc++.h>
using namespace std;
int n, m, a[200005], b[200005];
void solve() {
    cin>>n>>m;
    vector<pair<int,int> > g;
    for(int i=1;i<=n;i++) {
        cin>>a[i];
        g.push_back({a[i], 0});
    }
    int sum=0;
    for(int i=1;i<=n;i++) {
        cin>>b[i];
    }
    sort(b+1, b+n+1);
    for(int i=1;i<=n;i++) {
        sum+=b[i];
        g.push_back({sum, 1});
    }
    sort(g.begin(), g.end());
    priority_queue<int, vector<int>, greater<int> > q;
    int nxt=1, flag=0, ans=0;
    a[n+1]=m;
    for(auto tmp:g) {
        //cout<<"#"<<tmp.first<<" "<<tmp.second<<endl;
        if(tmp.second==1) {
            q.push(0);
        }
        else {
            flag=0;
            nxt++;
        }
        if(!q.empty()&&!flag) {
            
            int c=q.top();
            //cout<<c<<" "<<a[nxt]<<" "<<tmp.first<<endl;
            if(c<a[nxt]-tmp.first) {
                ans-=c; ans+=a[nxt]-tmp.first;
                q.pop(); q.push(a[nxt]-tmp.first);
                flag=1;
            }
        }
    }
    cout<<ans<<endl;
}
int main() {
    ios :: sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    int Case;
    cin >> Case;
    while (Case --) solve();
    return 0;
}
/*
3
3 10
1 5 9
1 2 3
3 10
1 5 9
1 1 4
3 10
1 5 9
1 5 10
*/