import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        int T = in.nextInt();
        while (T-->0){
            int n=in.nextInt();
            int m=in.nextInt();
            int [][]data=new int[n][2];
            int min=Integer.MAX_VALUE;
            for(int i=0;i<n;i++){
                data[i][0]=in.nextInt();
                data[i][1]=in.nextInt();
                int x = m/data[i][0];
                if(m%data[i][0]!=0) x++;
                min=Math.min(x*data[i][1],min);
            }

            System.out.println(min);
        }
    }
}