南阳97

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