#include <bits/stdc++.h>
using namespace std;

using ll = long long;
#define int ll
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
using pii = pair<int, int>;
using vi = vector<int>;
#define fi first
#define se second
#define pb push_back

const int N=1e5+100;

int a[N],b[N];
vector<int> my[N];

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);

    int t;
    cin>>t;
    while(t--)
    {
        int n,m;
        cin>>n>>m;
        for(int i=1;i<=n+1;i++)
            my[i].clear();
        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) {
                int j = upper_bound(a + 1, a + n + 1, b[i]) - a;
                my[j].pb(b[i]);
            }
        }
        a[n+1]=m;
        multiset<int,greater<>> s;
        int ans=0;
        for(int i=n+1;i>=1;i--)
        {
//            cout<<a[i-1]<<".."<<a[i]<<" -> ";
            if(my[i].empty()) {
//                cout<<"empty -> insert "<<a[i] - a[i - 1]<<"\n";
                s.insert(a[i] - a[i - 1]);
            }
            else
            {
                for(int j=1;j<my[i].size()&&!s.empty();j++)
//                    cout<<"add:"<<*s.begin()<<" ",
                    ans+=*s.begin(),
                    s.erase(s.begin());
                if(s.empty())
                    s.insert(0);
                int best=*s.begin();
                s.erase(s.begin());
                if(a[i]-my[i].front()>best) {
//                    cout<<"add-cur:"<<a[i] - my[i].front()<<",insert:"<<best + my[i].front() - a[i - 1]<<"\n";
                    ans += a[i] - my[i].front();
                    s.insert(best + my[i].front() - a[i - 1]);
                }
                else {
//                    cout<<"add-best:"<<best<<",insert:"<<a[i] - a[i - 1]<<"\n";
                    ans += best;
                    s.insert(a[i] - a[i - 1]);
                }
            }
        }
        cout<<ans<<"\n";
    }
}