#include<iostream>
#include<cmath>
using namespace std;
typedef long long LL;
typedef long double ldb;
const int N=400005;
const ldb eps=1e-15l;
int n,v;
LL standar;
struct People {
	LL s;
	int v;
} A[N];
bool check(ldb t) {
	ldb lowS=-1e13,uprS=1e13;
	for(int i=1; i<=n; i++) {
		if(A[i].s<0) {
			if(A[i].v*t+A[i].s>lowS) lowS=A[i].v*t+A[i].s; 
		} else {
			if(A[i].s-A[i].v*t<uprS) uprS=A[i].s-A[i].v*t; 
		}
	}
	return uprS<=lowS;
}
void solve() {
//	printf("%.8Lf\n",1e16l+5e-8l);
	scanf("%d%d",&n,&v);
	for(int i=1; i<=n; i++) {
		scanf("%lld%d",&A[i].s,&A[i].v);
	}
	ldb L=0,R=1e14,ans=0;
	while(R-L>eps) {
		ldb mid=(L+R)/2;
		if(check(mid)) {
			ans=mid;
			if(R-mid<eps)break;
			R=mid;
		}
		else {
			if(mid-L<eps)break;
			L=mid;
		}
	}
	printf("%.8Lf\n",ans*v);
}
int main() {
	int T;scanf("%d",&T);
	while(T--) solve();
	return 0;
}