#include <bits/stdc++.h>
using namespace std;
using LL = long long;
const int N = 1e5 + 10;

LL a[N], b[N], val[N];
void solve()
{
    int n, m;
    cin >> n >> m;
    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);

    deque <int> used;
    a[n + 1] = m;
    for(int i = 1; i <= n; i++) b[i] += b[i - 1];
    for(int i = 1; i <= n; i++) val[i] = a[i + 1] - a[i];
    int pa = n + 1, pb = n, sa = 0;
    while(pa > 0 && pb > 0) {
        while(a[pa] > b[pb]) sa++, pa--;
        used.push_front(b[pb]);
        if(used.size() > sa) used.pop_back();
        pb--;
    }

    pb = used.size();
    for(int i = used.size(); i >= 1; i--) {
        b[i] = used.back();
        used.pop_back();
    }
    pa = n + 1;
    LL ans = 0;

    priority_queue <LL> q;
    q.push(0);
    while(pa > 0 && pb > 0) {
        if(b[pb] >= m) {
            pb--;
            continue;
        }
        while(a[pa - 1] >= b[pb]) q.push(val[pa - 1]), pa--;
        if(q.top() >= a[pa] - b[pb]) {
            ans += q.top();
            q.pop();
        } 

        else {
            ans += a[pa] - b[pb];
            LL mx = q.top();
            q.pop();
            q.push(mx + b[pb] - a[pa - 1]);
            pa--;
        }
        pb--;
    }
    while(pb) {
        ans += q.top();
        q.pop();
        pb--;
    }
    cout << ans << '\n';
    
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    while(t--) solve();
    return 0;
}