#include<bits/stdc++.h>
using namespace std;
template <typename T> inline void read(T &x)
{
	x=0;short f=1;char c=getchar();
	for(;c<'0'||c>'9';c=getchar()) if(c=='-') f=-1;
	for(;c>='0'&&c<='9';c=getchar()) x=(x<<1)+(x<<3)+(c^48);
	x*=f;return;
}
#define double long double
const int N=4e5+5;
const double eps=1e-8;
#define ll long long
int n;
ll p[N],v[N],k;
bool check(double x)
{
	double maxx=-1e18,minx=1e18;
	for(int i=1;i<=n;++i)
		if(p[i]<0) maxx=max(maxx,p[i]+v[i]*x);
		else minx=min(minx,p[i]-v[i]*x);
	return minx<maxx;
}
int main()
{
	int T;read(T);
	while(T--)
	{
		read(n),read(k);
		for(int i=1;i<=n;++i)
			read(p[i]),read(v[i]);
		double l=0,r=1e12;
		while(r-l>eps)
		{
			double mid=(l+r)/2.0;
			if(check(mid)) r=mid;
			else l=mid;
		}
		printf("%.9Lf\n",l*k);
	} 
	return 0;
}