#include <bits/stdc++.h>
 
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using ld = long double;
using pld = pair<ld, ld>;

mt19937 rng((int) chrono::steady_clock::now().time_since_epoch().count());
    
const int MOD = 1e9 + 7;
const int MAXN = 4e5 + 5;
const ll INF = 2e12;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);
    int t;
    cin >> t;
    while(t--) {
        int n;
        ld vl;
        cin >> n >> vl;
        vector <pld> pos, neg;
        ld mx = 0;
        for(int i = 1; i <= n; i++) {
            ld p, v;
            cin >> p >> v;
            mx = max(mx, v);
            if(p < 0) neg.push_back({p, v});
            else pos.push_back({p, v});
        }
        ld ini = 0, fim = INF;
        for(int i = 0; i < 80; i++) {
            ld m = (ini + fim) / 2;
            ld mx = -INF, mn = INF;
            for(auto cur : neg) {
                mx = max(mx, cur.first + cur.second * m);
            }
            for(auto cur : pos) {
                mn = min(mn, cur.first - cur.second * m);
            }
            if(mx >= mn) fim = m;
            else ini = m;
        }
        cout << ini * vl << '\n';
    }
    return 0;
}