#include<cstdio>
#include<iostream>
using namespace std;
const int o=4e5+10;const long double inf=1e12;
int z,n,v,v_[o];long long p[o];long double l,r,md,mx,mn;
int main(){
	for(scanf("%d",&z);z--;printf("%.9Lf\n",l*v)){
		scanf("%d%d",&n,&v);
		for(int i=1;i<=n;++i) scanf("%lld%d",&p[i],&v_[i]);
		l=0;r=inf;
		for(int T=100;T--;){
			md=(l+r)/2;mx=-inf;mn=inf;
			for(int i=1;i<=n;++i)
				if(p[i]<0) mx=max(mx,p[i]+v_[i]*md);
				else mn=min(mn,p[i]-v_[i]*md);
			if(mn<mx) r=md;
			else l=md;
		}
	}
	return 0;
}