#include<iostream>
#include<string.h>
using namespace std;
int test,n,m;
int calcnt(int cost,int m)
{
    int cnt=cost/m;
    if(cnt*m<cost)
    {
        cnt++;
    }
    return cnt;
}
int main()
{
    cin>>test;
    while(test--)
    {
        n=0;
        m=0;
        int ans=99999999;
        cin>>n>>m;
        for(int i=0;i<n;i++)
        {
            int x,y;
            cin>>x>>y;
            int cnt=calcnt(m,x);
            if(ans>cnt*y)
            {
                ans=cnt*y;
            }
        }
        cout<<ans<<endl;
    }
 }