#include <bits/stdc++.h>
using namespace std;
#define ll long long
vector<pair<ll, int>> f, g;
using db = long double;
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);
    }
    db l = 0, r = 1e12;
    for (int i = 1; i <= 120; ++i) {
        db mid = (l + r) / 2;
        db 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;
    }
    cout << fixed << setprecision(15) << (l + r) / 2 * v0 << '\n';
}
int main() {
    int t;
    scanf("%d", &t);
    while (t--) {
        solve();
    }
    return 0;
}