#include"bits/stdc++.h"

using lint = int64_t;

constexpr int MOD = int(1e9) + 7;
constexpr int INF = 0x63636363;
constexpr int NINF = 0xcfcfcfcf;
constexpr lint LINF = 0x6363636363636363;

using namespace std;

using ld = double;
void solve(){
    int n; cin>>n;
    ld ini_v;
    cin>>ini_v;
    vector<pair<ld, ld>> left, right;
    for(int i =0; i<n; i++){
        ld p, v;
        cin>>p>>v;
        if(p < 0) left.emplace_back(p, v);
        else right.emplace_back(p, v);
    }
    ld lo = 0, hi = 3000000000001;
    for(int it = 300; it--; ){
        ld mid = (lo + hi) / 2;
        ld min_right = 3000000000001;
        ld max_left = -3000000000001;
        for(auto [p, v]: left){
            ld cur_p = p + v * mid;
            max_left = max(max_left, cur_p);
        }
        for(auto [p, v]: right){
            ld cur_p = p - v * mid;
            min_right = min(min_right, cur_p);
        }
        if(min_right < max_left) hi = mid;
        else lo = mid;
    }
    cout<<fixed<<setprecision(20)<<hi * ini_v<<"\n";
}   

int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    int t; cin>>t;
    while(t--){
        solve();
    }
    return 0;
}