#include<bits/stdc++.h>
using namespace std;
double x,a,y,b;
int main(){
    cin>>x>>a>>y>>b;
    printf("%.2lf",(x*a-y*b)/(a-b));
	return 0;
}

经典问题——牛吃草。

#include<bits/stdc++.h>
using namespace std;
double x,a,y,b;
int main(){
    cin>>x>>a>>y>>b;
    printf("%.2lf",(x*a-y*b)/(a-b));
	return 0;
}