#include<bits/stdc++.h>

#pragma GCC optimize ("Ofast")

using namespace std;

#define rep(i,a,b) for(ll i = a; i<b;i++)
#define rrep(i,a,b) for(ll i = b-1; i>=a;i--)
#define trav(x,a) for(auto &x: a)
#define all(v) v.begin(),v.end()
#define sz(v) ll(v.size())

typedef long long ll;
typedef vector<ll> vl;
typedef pair<ll,ll> pll;
typedef long double ld;

void solve(){
    ll n;
    ld v;
    cin>>n>>v;

    vector<pair<ld,ld>> slopes;
    rep(i,0,n) {
        ld p,vp;
        cin>>p>>vp;
        if(p<0){
            slopes.emplace_back(p,vp);
        } else {
            slopes.emplace_back(p,-vp);
        }
    }
    
    ld lw=0,hi=1e18;
    
    rep(_,0,400){
        ld mid = (lw+hi)/2;
        ld l = -1e18;
        ld r = 1e18;

        for(auto [k,m]:slopes){
            if(k<0){
                l = max(l, k+m*mid);
            } else {
                r = min(r, k+m*mid);
            }
        }

        if(l<r){
            lw = mid;
        } else {
            hi = mid;
        }
    }

    cout<<setprecision(18)<<fixed<<((lw+hi)/2)*v<<"\n";
}

int main(){
    cin.tie(0);
    ios_base::sync_with_stdio(0);

    ll t; cin>>t;
    while(t--) solve();
}