#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define MP make_pair
mt19937 rnd(time(0));
const int MAXN=4e5+5;
int n,v;
ll p[MAXN],a[MAXN]; 
bool check(long double x){
	long double le=-1e18,ri=1e18;
	for(int i=1;i<=n;i++) 
		if(p[i]<0) le=max(le,p[i]+a[i]*x);
		else ri=min(ri,p[i]-a[i]*x);
	return le>=ri;
}
void solve(){
	cin>>n>>v;
	for(int i=1;i<=n;i++) cin>>p[i]>>a[i];
	long double l=0,r=1e12,mid;
	for(int i=1;i<=100;i++){
		mid=(l+r)*0.5;
		if(check(mid)) r=mid;
		else l=mid;
	}
	cout<<setprecision(12)<<l*v<<endl;
}
int main(){
	ios::sync_with_stdio(false);
	int _;cin>>_;
	while(_--) solve();
}