#include <bits/stdc++.h>
using namespace std;
const int N = 2e6 + 10;
#define int long long
double x[N], w[N];
int n;
bool check(double mid)
{
    double r1 = -1e12, r2 = 1e12;
    for (int i = 1; i <= n; i++)
    {
        if (x[i] < 0)
        {
            r1 = max(r1, x[i] + mid * w[i]);
        }
        else
            r2 = min(r2, x[i] - mid * w[i]);
    }

    return r1 > r2; // 相遇
}
void solve()
{
    cin >> n;
    double v;
    cin >> v;
    for (int i = 1; i <= n; i++)
    {
        cin >> x[i] >> w[i];
    }
    double l = 0, r = 1e12;
    for(int i = 1; i <= 600; ++i)
    {
        double mid = (l + r) / 2;
        if (check(mid))
            r = mid;
        else
            l = mid;
    }
    double ans = l * v;
    printf("%.12lf\n", ans);
}
signed main()
{
    int t = 1;
    cin >> t;
    while (t--)
        solve();

    // system("pause");
}