#include <bits/stdc++.h>
using namespace std;
void te() {
	int n, k;
	cin >> n >> k;
	int ans = 0;
	while(n--) {
		int minutes, cost;
		cin >> minutes >> cost;
		int free = min(minutes, k);
		k -= free;
		minutes -= free;
		ans += minutes * cost;
	}
	cout << ans << "\n";
}
int main() {
	int T;
	cin >> T;
	while(T--) te();
}