#include <bits/stdc++.h>
#define pb emplace_back

#define ls(x) (x << 1)
#define rs(x) (x << 1 | 1)

using namespace std;

using LDB = long double;
using DB = double;
using LL = long long;

void solve()
{
	LDB eps = 1e-12;
	int n;
	LDB v;
	scanf("%d%Lf", &n, &v);
	vector<LDB> pos(n + 1, 0), speed(n + 1, 0);
	for(int i = 1; i <= n; ++i){
		scanf("%Lf%Lf", &pos[i], &speed[i]);
	}

	LDB l = 0.0, r = 1e12, mid = 0, round = 0;
	while(r - l > eps){
		++round;
		mid = (l + r) / 2;
		if(r - l > eps){
			if(r - mid <= eps){
				l = mid;
				break;
			}
			else if(mid - l <= eps){
				r = mid;
				break;
			}
		}
		
		
		LDB maxl = -1e12 - 1, minr = 1e12 + 1;
		for(int i = 1; i <= n; ++i){
			if(pos[i] < 0)
				maxl = max(maxl, pos[i] + mid * speed[i]);
			else
				minr = min(minr, pos[i] - mid * speed[i]);
		}
		
		if(maxl >= minr)
			r = mid;
		else
			l = mid;
		// printf("%.12Lf %.12Lf %.12Lf\n", l, r, r - l);
		

		
	}
	printf("%.12Lf\n", l * v);
}

int main()
{
	// ios::sync_with_stdio(0);
	// cin.tie(0);

	int T;
	scanf("%d", &T);
	while(T--){
		solve();
	}
	return 0;
}