/*
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*/
#include <bits/stdc++.h>
#define fastIO ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define MOD 1000000007LL
#define MOD2 998244353LL
#define endl '\n'
#define INFINITE 2147483647LL
#define INFINITE2 9223372036854775807
#define llll pair<ll,ll>
#define fi first
#define se second
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

using namespace std;

ll n,v;
ll a[400005],b[400005];
ld l,r,ma,mi;

bool check(ld k)
{
    //cout << k << ": ";
    ld x=-INFINITE2,y=INFINITE2;
    for(int i=1;i<=n;i++)
    {
        if(a[i]<=0) x=max(x,a[i]+k*b[i]);
        else y=min(y,a[i]-k*b[i]);
    }
    //cout << x << " " << y << endl;
    if(x>=y) return false;
    return true;
}

void solve()
{
    ld ans=0;
    l=r=ma=mi=0;
    cin >> n >> v;
    for(int i=1;i<=n;i++)
    {
        cin >> a[i] >> b[i];
        ma=max(ma,(ld)a[i]);
        mi=min(mi,(ld)a[i]);
    }
    l=0,r=ma-mi;
    ll temp=0;
    while(l<=r&&temp<=1000000)
    {
        ld mid=(l+r)/2.0;
        if(check(mid))
        {
            ans=mid;
            l=mid+0.00000001;
        }
        else r=mid-0.00000001;
        temp+=n;
    }
    cout << setprecision(15) << fixed << ans*v << endl;
}

int main()
{
    fastIO
    //freopen("hanhhhh.inp","r",stdin);
    //freopen("hanhhhh.out","w",stdout);
    ll t=1;
    cin >> t;
    while(t--)
    solve();
    return 0;
}