#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define openr() freopen("input.txt","r",stdin)
#define openw() freopen("output.txt","w",stdout)
#define mp make_pair
#define fi first
#define se second
#define int long long int
#define double long double

using namespace std;
using namespace __gnu_pbds;
template <typename T>
using ordered_set=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;

const int inf=1e15;
const int mod= 1000000007;


void show()
{
    int n,v;    cin>>n>>v;
    vector<pair<int,double>>a(n);
    for(int i=0;i<n;i++)
    {
        cin>>a[i].fi>>a[i].se;
    }
    sort(a.begin(), a.end());
    double r= max(fabs(a[0].fi), fabs(a[n-1].fi));
    double l=0;
    double res= 0;
    double thres_hold= 0.0000000001;
    while(l <  r && r - l  > thres_hold){

        double temp= l+r;
        double mid= (l+r)/2.0;
        double ls=-inf;
        double rs= inf;
        for(int i=0;i<n;i++)
        {
            // fi pos
            // se vel
            double dis= a[i].se * mid;
            if(a[i].fi < 0) ls= max(ls, a[i].fi + dis);
            else rs= min(rs, a[i].fi - dis);
        }
        if(ls < rs )
        {
            // tang time
            res= max(res, mid);
            l= mid+thres_hold;
        }
        else if(ls == rs)
        {
            res= mid;
            break;
        }
        else    {
            r= mid - thres_hold;
        }
    }
    cout<<fixed<<setprecision(10)<<res*v;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    //openr();
    int tc; cin>>tc;
    while(tc--)
    {
        show();
        cout<<"\n";
    }
    return 0;
}