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

using LD = long double;
const LD eps = 1e-8;
int sgn(LD x){return fabs(x)<=eps ? 0 : (x>eps ? 1 : -1);}

const int N = 4e5+5;
int t, n, p[N], v[N];
const LD INF = 1e18;

bool check(LD x){
	LD mx=-INF, mn=INF;
	for (int i=1; i<=n; ++i){
		if (p[i]>0) mn=min(mn, p[i]-v[i]*x);
		else mx=max(mx, p[i]+v[i]*x);
	}
	return sgn(mx-mn)<0;
}
signed main(){
	ios::sync_with_stdio(0); cin.tie(0);
	cout << setiosflags(ios::fixed) << setprecision(10);
	cin >> t;
	while (t--){
		cin >> n >> v[0];
		for (int i=1; i<=n; ++i) cin >> p[i] >> v[i];
		LD L=0.0L, R=1e13;
		for (int tt=0; tt<200; ++tt){
//			printf("L=%Lf R=%Lf\n", L, R);
			LD M  = (R+L)*0.5L;
			if (check(M)) L=M;
			else R=M;	
		}
		cout << L*v[0] << '\n';
	}
	return 0;	
}