#include<bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pf push_front
#define LC k<<1
#define RC k<<1|1
#define IO cin.sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define rep(i,a,n) for (int i = a; i < n; i++)
#define repn(i,a,n) for (int i = a; i <= n; i++)
#define per(i,a,n) for (int i = (n) - 1; i >= a; i--)
#define pern(i,a,n) for (int i = n; i >= a; i--)

typedef long long LL;
typedef long double LD;
typedef unsigned long long ull;
typedef pair<int, int> PII;
typedef pair<int, LL> PIL;
typedef pair<LL, int> PLI;
typedef pair<double, double> PDD;
typedef pair<ull, ull> PUU;
typedef pair<LL, LL> PLL;

const int N = 410000;
const int M = 1100000;
const int mod = 1e9+7;
const int inf = (int)1e9;
const LL INF = 1e18;
const double eps = 1e-9;

mt19937_64 Rand((unsigned long long)new char);
#define rand Rand

int T, n;
double w, p[N], v[N];
int check(double x) {
	double mx = -INF, mn = INF;
	repn(i, 1, n) {
		if (p[i] < 0) mx = max(mx, p[i] + v[i] * x);
		else mn = min(mn, p[i] - v[i] * x);
	}
	return mx > mn;
}
int main() {
	IO;
	cin >> T;
	while (T--) {
		cin >> n >> w;
		repn(i, 1, n) cin >> p[i] >> v[i];
		double l = 0, r = 1e13;
		repn(rnd, 1, 100) {
			double mid = (l + r) / 2;
			if (check(mid)) r = mid;
			else l = mid;
		}
		cout << fixed << setprecision(15) << l * w << "\n";
	}
	return 0;
}