#include<bits/stdc++.h>
using namespace std;
#define ll long long
vector<pair<ll,int> > f,g;
void solve()
{
    ll x;
    int v,n,v0;
    scanf("%d%d",&n,&v0);
    f.clear();
    g.clear();
    for (int i=1;i<=n;++i)
    {
        scanf("%lld%d",&x,&v);
        if (x>0)
            f.emplace_back(x,v);
        else
            g.emplace_back(x,v);
    }
    double l=0,r=1e12;
    for (int i=1;i<=80;++i)
    {
        double mid=(l+r)/2;
        double mnf=1e12,mxg=-1e12;
        for (auto [x,v]:f)
            mnf=min(mnf,x-v*mid);
        for (auto [x,v]:g)
            mxg=max(mxg,x+v*mid);
        if (mnf<mxg)
            r=mid;
        else
            l=mid;
    }
    printf("%.10lf\n",(l+r)/2*v0);
}
int main()
{
    int t;
    scanf("%d",&t);
    while (t--)
    {
        solve();
    }
    return 0;
}