#include <iostream>
#include <iomanip>
#include <vector>
#include <limits>
using namespace std;

int main() {
    int tc;
    cin >> tc;

    while (tc != 0) {
        tc--;

        double n, v;
        cin >> n >> v;

        vector<pair<double, double>> a;
        for (int i = 0; i < n; i++) {
            double pi, vi;
            cin >> pi >> vi;
            a.push_back(make_pair(pi, vi));
        }

        double l = 0;
        double r = 1e12;
        double res = 0;
        double e = 0.0000000001;
        int cnt = 100;

        while ( cnt != 0) {
            cnt--;
            double mid = (l + r) / 2;
            double ls = -1e18;
            double rs = 1e18;

            for (int i = 0; i < n; i++) {
                double temp1 = a[i].first;
                double temp2 = a[i].second;
                double dis = temp2 * mid;

                if (temp1 < 0) {
                    ls = max(ls, temp1 + dis);
                } else if (temp1 == temp2) {
                    rs = mid;
                    break;
                } else {
                    rs = min(rs, temp1 - dis);
                }
            }

            if (ls <= rs) {
                res = max(res, mid);
                l = mid ;
            } else {
                r = mid ;
            }
        }

        cout << fixed << setprecision(10) << res * v << endl;
    }

    return 0;
}