10opencup

#include <iostream>
#include <vector>
#include <string.h>
#include <algorithm>
#include "math.h"
#include <map>
#include "bits/stdc++.h"
using namespace std;
class Tpair {
public:
    double t;
    double a;
    double S;
};
int main() {
    int test;
    cin >> test;
    double v0 = 0;
    for (int d = 0; d < test; d++) {
        int n, qq;
        cin >> n >> qq;double l=qq;
        l *= 1000;
        map<double, Tpair> a;
        for (int i = 0; i < n; i++) {
            int as, t;
            Tpair b;
            cin >> as >> t;
            double S = (double)as*t*t/2;
            double V = (double)S/t;
            b.a = as;b.S = S;b.t = t;
            a[V] = b;
        }
        map<double, Tpair> :: const_iterator it = a.end();
        it--;
        double ansT = 0;
        for (map<double, Tpair> :: const_iterator id = it; id !=a.begin(); id--) {
            //v0 += id->first*id->second.a;
            double St = (id->second.a)*(pow(id->second.t, 2))/2 + v0*id->second.t;

            if (St <= l) {
                l -= St;
               // v0 += id->first * id->second.a;
                 ansT+=id->second.t;
            }
            else {
                ansT+=sqrt(2*l/id->second.a);
                l = 0;
            }
            v0 += id->second.a * id->second.t;            //cout << St << " " << l << " " << v0 << " " << ansT << endl;
        }
        if (l > 0) {
            map<double, Tpair>::const_iterator id = a.begin();
            double St = (double) id->second.a * pow(id->second.t, 2) / 2 + (double) v0 * id->second.t;
            if (St <= l) {
                l -= St;
                // v0 += id->first * id->second.a;
                ansT+=id->second.t;
            } else {
                ansT += sqrt(2 * l / id->second.a);
                l = 0;
            }
            v0 += id->second.t * id->second.a;  // cout << St << " " << l << " " << v0 << " " << ansT << endl;
        }
        if (l > 0) {
           // cout << endl << l << " " << v0 <<" " <<  ansT << endl;
           ansT += l/v0;
        }
        //v0 += id->first * id->second.a;
       // ansT*=100;ceil(ansT);ansT/=100;
        //cout << ceil(ansT*100)/100;
        printf("%0.2lf\n", ceil(100*ansT)/100);
    //    printf("%0.2lf\n", ansT);

    }
    return 0;
}