#include<bits/stdc++.h>
using namespace std;

int main()
{
	int n;
	cin>>n;
	int m,x,y,z;
	double t,s;
	while(n--)
	{
		cin>>m>>x>>y>>z;
		t = x*m*1.00/(y-x);
		s = t*z;
		cout<<fixed<<setprecision(2)<<s<<endl;
	}
}