#include <bits/stdc++.h>
using namespace std;
#define M 400005
using ll = long long;
int n,v;
ll P[M];
int V[M];
bool check(double t){
    double mx=-1e20,mi = 1e20;
    for(int i=1;i<=n;i++){
        if(P[i]<0) mx = max(mx,P[i] + V[i]*t);
        else mi = min(mi,P[i] - V[i]*t);
    }
    return mi<mx;
}
int main(){
    int Cas;cin>>Cas;
    while(Cas--){
        scanf("%d%d",&n,&v);
        for(int i=1;i<=n;i++)
            scanf("%lld%d",&P[i],&V[i]);
        double l = 0, r = 2e12,ans=-1;
        for(int _=1;_<=100;_++){
            double mid = (l+r)/2;
            if(check(mid))ans=mid,r=mid;
            else l=mid;
        }
        printf("%.10lf\n",ans*v);
    }
    return 0;
}