#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 2137
#endif

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int tt;
  cin >> tt;
  while (tt--) {
    int n, v;
    cin >> n >> v;
    vector<pair<ll, ll>> a, b;
    for (int i = 0; i < n; i++) {
      ll p, vv;
      cin >> p >> vv;
      (p > 0 ? a : b).push_back({p, vv});
    }
    ld lo = 0;
    ld hi = 2.5e12;
    for (int it = 0; it < 100; it++) {
      ld mid = (lo + hi) / 2;
      ld mx = -2e18;
      ld mn = 2e18;
      for (auto [p, q] : a) {
        mn = min(mn, p - mid * q);
      }
      for (auto [p, q] : b) {
        mx = max(mx, p + mid * q);
      }
      if (mn <= mx) {
        hi = mid;
      } else {
        lo = mid;
      }
    }
    ld t = (lo + hi) / 2;
    cout << fixed << setprecision(10) << t * v << '\n';
  }
}