#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b) {
    int x = 1;
    a %= M;
    while (b) {
        if (b & 1) x = (x * a) % M; 
        a = (a * a) % M;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************



vector<int> boxes;
vector<int> unitPerBox;

int consistency(int n, int t) {
	
	vector<pair<int,int>> p;
	for(int i=0; i<n; i++){
		p.push_back({unitPerBox[i], boxes[i]});
	}
	
	sort(begin(p), end(p), greater<pair<int,int>>());
	
	int ans = 0;
	for(int i=0; i<n; i++){
		int unit = p[i].first;
		int box = p[i].second;
		
		int k = min(box, t);
		
		ans += k*unit;
		t -= k;
		
	}

	return ans;
	
}













// boxes[]
// unitPerBox[]

int practice(int n, int t) {
	
	return 0;
}


void solve() {
    
	int n, t;
	cin >> n >> t;
	
	boxes.resize(n);
	unitPerBox.resize(n);
	for(int i=0; i<n; i++) cin >> boxes[i];
	for(int i=0; i<n; i++) cin >> unitPerBox[i];

    cout << consistency(n, t)  << endl;
    // cout << consistency(n, t) << " -> " << practice(n, t) << endl;

}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}