# include <bits/stdc++.h>
# define int long long
# define imax(a , b) ((a) > (b) ? (a) : (b))
# define imin(a , b) ((a) < (b) ? (a) : (b))
# define rl ro << 1
# define rr ro << 1 | 1
using namespace std;
const int N = 4e5 + 511;
int n;
struct tag
{
	double x , v;
}a[N];

bool check(double k){
	
	double l = -1e12 , r = 1e12;
	for (int i = 1; i <= n; ++i)
	{
		if (a[i].x > 0) r = imin(r , a[i].x - k * a[i].v);
		if (a[i].x < 0) l = imax(l , a[i].x + k * a[i].v);
	}
	
	if ((r - l) >= 1e-15) return 1;
	return 0;
}
void solve()
{
	double V;
	cin>>n>>V;

	for (int i = 1; i <= n; ++i){
		cin>>a[i].x>>a[i].v;
	}

	double L = 0 , R = 1e12;
	for (int i = 1; i <= 600; ++i){
		double mid = (L + R) / 2.0;

		if (check(mid)) L = mid;
					else R = mid;
	}

	cout<<fixed<<setprecision(12)<<L * V<<"\n";
}
signed main()
{
	std::ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int T = 1;
	cin>>T;
	while (T--) solve();
}