#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define ll long long int

ll read(){
    char ch=getchar();
    ll sum=0;
    bool ttt=false;
    while(!isdigit(ch)) ttt=(ch=='-'),ch=getchar();
    while(isdigit(ch)) sum=(sum<<3)+(sum<<1)+(ch-'0'),ch=getchar();
    return ttt?-sum:sum;
}

int tst;
int n,m;
int a,b,ans;

int dv(int x, int y){
    if(x%y) return x/y+1;
    return x/y;
}

int main(){
    tst=read();
    for(int i=1;i<=tst;i++){
        n=read(),m=read(),ans=0x7fffffff;
        for(int j=1;j<=n;j++) a=read(),b=read(),ans=min(ans,dv(m,a)*b);
        printf("%d\n",ans);
    }
    return 0;
}