#include "bits/stdc++.h"

using namespace std;
using lint = int64_t;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    int t; cin>>t;
    while(t--){
        int n; cin>>n;
        using ld = long double;
        ld v; cin>>v;
        vector<pair<ld, ld>> pl, pr;
        pl.reserve(n);
        pr.reserve(n);
        for(int i =0; i<n; i++){
            ld p, v;
            cin>>p>>v;
            if(p < 0)
                pl.push_back({p, v});
            else
                pr.push_back({p, v});
        }
        ld left = 0, right = 3000000000005;
        int it = 500;
        while(it--){
            ld m = (left + right) / 2;
            ld maxil = -1e12l;
            ld minr = 1e12l;
           // cout<<"mid "<<m<<"\n";
            for(const auto &[p, v] : pl){
                maxil = max<ld>(maxil, p + m * v);
                //cout<<p + m * v<<" ";
            }
           // cout<<" ||| ";
            for(const auto &[p, v] : pr){
                minr = min<ld>(minr, p - m * v);

                //cout<<p - m * v<<" ";
            }
           // cout<<"\n";
            if(maxil < minr) left = m;
            else right = m;
        }
        cout<<fixed<<setprecision(20)<<left*v<<"\n";
    }
    return 0;
}