#include<iostream>
#include<cmath>
using namespace std;
typedef long long LL;
typedef long double ldb;
const int N=400005;
const ldb eps=1e-9l;
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() {
    scanf("%d%d",&n,&v);
    ldb mnt=1e13;
    for(int i=1; i<=n; i++) {
        scanf("%lld%d",&A[i].s,&A[i].v);
        mnt=min(mnt,fabs(1.0l*A[i].s)/A[i].v);
    }
    ldb L=0,R=1e14,ans=0,lastL=0,lastR=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;
}