#include <bits/stdc++.h>

#define maxn 400005
#define ll long long
#define ld long double

using namespace std;

int n;
ll d;
ll p[maxn];
ll v[maxn];

int main() {
	int T;
	scanf("%d", &T);
	while (T--) {
		scanf("%d%lld", &n, &d);
		for (int i = 1; i <= n; i++) scanf("%lld%lld", &p[i], &v[i]);
		ld l = 0, r = 2e12, mid;
		for (int i = 1; i <= 200; i++) {
			mid = (l + r) / 2.0;
			ld mn = 1e18, mx = -1e18;
			for (int j = 1; j <= n; j++) {
				if (p[j] < 0) mx = max(mx, p[j] + v[j] * mid);
				else mn = min(mn, p[j] - v[j] * mid);
			}
//			cout<<mn<<" "<<mx<<endl;
			if (mx >= mn) r = mid;
			else l = mid;
		}
		printf("%.10Lf\n", l * d);
	}
	return 0;
}