#include <bits/stdc++.h>
//G
using namespace std;
double t, calc, enc, tn, tp, t2;
vector <double> polvn (400001);
vector <double> polpn (400001);
vector <double> polvp (400001);
vector <double> polpp (400001);

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    long long int z, n, nn, np, v, pi, vi, mpn, mpp, it, mvp, mvn;
    cin >> z;
    while (z--){
        it = 0;
        mpn = -100000000000000; 
        mpp = 100000000000000;
        np = 0;
        nn = 0;
        cin >> n >> v;
        while (n--){
            cin >> pi >> vi;
            if (pi < 0){
                polpn[nn] = pi;
                polvn[nn] = vi;
                if (pi > mpn){
                    mpn = pi;
                    mvn = vi;
                }
                nn ++;
            } else{
                polpp[np] = pi;
                polvp[np] = vi;
                if (pi < mpp){
                    mpp = pi;
                    mvp = vi;
                }
                np ++;
            }
        } 
        t = (mpp - mpn)*1.0/(mvp + mvn);
        tn = t;
        tp = t;
        while (it < 99){
            enc = mpn + t*mvn;
            for (int i = 0; i < np; i++){
                if ((polpp[i]- enc)/(1.0*polvp[i]) < tp){ 
                    tp = (abs(polpp[i] - enc))/(1.0*polvp[i]);
                    mpp = polpp[i];
                    mvp = polvp[i];
                }
            } for (int i = 0; i < nn; i++){
                if ((enc - polpn[i])/(1.0*polvn[i]) < tn){ 
                    tn = (abs(enc - polpn[i]))/(1.0*polvn[i]);
                    mpn = polpn[i];
                    mvn = polvn[i];
                }
            } t2 = (mpp - mpn)*1.0/(mvp + mvn);
            if (t - t2 < 0.00000001) break;
            it ++;
            t = t2;
        }
        cout << fixed << setprecision(8); 
        cout << t*v << "\n";

    } return 0;
}