#include <bits/stdc++.h>
#define X first
#define Y second
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef long long lint;

const int N = 100005;

int n, m, a[N], b[N];

void solve ()
{
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++) {
        scanf("%d",&a[i]);
    }
    a[n+1] = m;
    for(int i=1;i<=n;i++) {
        scanf("%d",&b[i]);
    }
    sort(b+1, b+1+n);
    vector<pii> gugan;
    vector<int> jum;
    for(int i=1;i<=n;i++) {
        gugan.push_back({a[i], a[i+1]});
    }
    for(int i=1;i<=n;i++) {
        b[i] += b[i-1];
        if (b[i] < m) jum.push_back(b[i]);
        else break;
    }
    priority_queue<int> prof;
    long long ans = 0;
    int gi = (int)gugan.size()-1;
    int zp = 0, zb = 0;
    for(int i=(int)jum.size()-1;i>=0;i--) {
        int cj = jum[i];
        while(gi >= 0 && cj <= gugan[gi].X) {
            prof.push(gugan[gi].Y - gugan[gi].X - zp + zb);
            zp = 0;
            zb = 0;
            gi--;
        }
        int tp = prof.top();
        if (gi >= 0 && tp < gugan[gi].Y - cj - zp + zb) {
            ans += gugan[gi].Y - cj - zp + zb;
            zp = gugan[gi].Y - cj;
            zb = tp;
        }
        else {
            ans += tp;
        }
        prof.pop();
    }
    printf("%lld\n", ans);
}

int main()
{
    //ios_base::sync_with_stdio(false); cin.tie(NULL);

    int TC;
    cin >> TC;
    while(TC--)
    {
        solve();
    }
}