#include<bits/stdc++.h>
using namespace std;
#define int long long
#define sc(x) scanf("%lld",&x);
int x,y;
signed main()
{
 int t;
 sc(t)
 while(t--){

 int n,m;
    sc(n)sc(m)
    int ans = -1;
    for(int i=0;i<n;i++){
        sc(x)sc(y)
        int t = (m/x+(m%x?1:0))*y;
        if(ans == -1 || ans > t){
            ans = t;
        }
    }
    cout<<ans<<'\n';
}
}