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

#define int long long  

void solve() {
	int n, m;
	cin >> n >> m;

	vector<int> a(n + 2);
	a[0] = 0, a[n + 1] = m;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	vector<int> b(n + 1);
	for (int i = 1; i <= n; i++) {
		cin >> b[i];
		b[i] += b[i - 1];
	}
	int j = n;
	while (j >= 1 && b[j] > m) {
		j--;
	}
	priority_queue<int> q;
	int ans = 0;
	for (int i = n; i >= 0; i--) {
		int l = a[i], r = a[i + 1];
		vector<int> t;
		while (j >= 1 && b[j] >= l) {
			t.push_back(b[j]);
			j--;
		}
		if (!t.size()) {
			q.push(r - l);
			continue;
		}
		for (int i = 0; i < (int)t.size() - 1; i++) {
			if (q.empty()) {
				break;
			}
			ans += q.top();
			q.pop();
		}
		if (q.empty()) {
			ans += r - t.back();
			q.push(t.back() - l);
			continue;
		}
		if (r - t.back() <= q.top()) {
			ans += q.top();
			q.pop();
			q.push(r - l);
		} else {
			ans += r - t.back();
			auto s = q.top();
			q.pop();
			q.push(s + t.back() - l);
		}
	}

	cout << ans << "\n";
}

signed main() {  
    ios::sync_with_stdio(false);
    cin.tie(nullptr);  

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

    return 0;
}