#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
    int x,a,y,b;
    double z;
    cin>>x>>a>>y>>b;
    z=(y*b-x*a)/(b-a);
    cout<<setiosflags(ios::fixed)<<setprecision(2);
    cout<<z<<endl;
    return 0;
}

制作不易，点个赞再拿走嘛

#include<bits/stdc++.h> using namespace std; int main(){ int x,a,y,b; float n; cin >> x >> a >> y >> b; n= (by - ax) / (b - a); cout << fixed << setprecision(2) << n; return 0; }

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

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

int main() { int x, a, y, b; double z; cin >> x >> a >> y >> b; z = (1.0 * x * a - y * b) / (1.0 * a - b); printf("%.2w", z); return 0; }