C :

#include<stdio.h>
main()
{
	float n,m,z,y,x;
	float result;
	scanf("%f",&n);
	while(n--)
	{
		scanf("%f%f%f%f", &m, &x, &y, &z);
		result=x*m/(y-x)*z;
		printf("%.2f\n",result);
	}
} 

C++ :

#include <stdio.h> 
int main() 
{ 
    int n , x ,m , y ,z; 
    double length,chaju,time; 
    scanf("%d",&n); 
    while(n--) 
    { 
        scanf("%d%d%d%d",&m,&x,&y,&z); 
        chaju = x * m ; 
        time = chaju / (y-x); 
        length = z * time ; 
        printf("%.2f\n",length); 
    } 
}