#include <iostream>
using namespace std;

int T;
int n,k;
int tt,dd;
int main(){
	//freopen("00.txt","r",stdin);
	//freopen("00o.txt","w",stdout);
	cin>>T;
	while(T--){
		cin>>n>>k;
		int sol=0;
		for(int i=0;i<n;i++){
			cin>>tt>>dd;
			if(tt>k){
				tt-=k;
				k=0;
			} else {
				k-=tt;
				tt=0;
			}
			sol+= tt*dd;
		}
		cout<<sol<<endl;
	}
}