#include <bits/stdc++.h>
#define int long long
using namespace std;

string to_string(string s) { return s; }
template <typename T> string to_string(T v) {
  bool first = true;
  string res = "[";
  for (const auto &x : v) {
    if (!first)
      res += ", ";
    first = false;
    res += to_string(x);
  }
  res += "]";
  return res;
}

void dbg_out() { cout << endl; }
template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) {
  cout << ' ' << to_string(H);
  dbg_out(T...);
}

#ifdef DEBUG
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif

void solve() {

  int nbPoliciers;
  cin >> nbPoliciers;
  int vitesse;
  cin >> vitesse;

  vector<pair<int, int>> gauche, droite;
  for (int i = 0; i < nbPoliciers; ++i) {
    int pos, v;
    cin >> pos >> v;
    if (pos > 0)
      droite.emplace_back(pos, v);
    else
      gauche.emplace_back(pos, v);
  }

  double lo = 0, up = 1e18;
  for (int it = 0; it < 200; ++it) {
    double mid = (lo + up) / 2;

    double maxL = -1e18, minR = 1e18;
    for (auto [pos, v] : gauche)
      maxL = max(maxL, pos + v * mid);
    for (auto [pos, v] : droite)
      minR = min(minR, pos - v * mid);
    if (maxL < minR)
      lo = mid;
    else
      up = mid;
  }
  cout << setprecision(15) << fixed << lo * vitesse << '\n';
}

signed main(void) {
  ios_base::sync_with_stdio(false);
  cin.tie(0);

  int nbTests;
  cin >> nbTests;
  for (int iTest(0); iTest < nbTests; ++iTest)
    solve();
}