C :

#include <stdio.h>
int main(){
    int a;
    scanf("%d",&a);
    
   float q;
    if(a <= 10){
    	q = 2.5;
    }else{
    	q = 2.5 + (a-10) * 1.5;
    }
    
    printf("%.2f",q);
    return 0;
}

C++ :

#include<iostream>
#include<iomanip>
using namespace std;
int main(){
	double x,i;
	cin>>i;
	if(i<=10){
		x=2.5;
	}else if(i>10){
		x=2.5+(i-10)*1.5;
	}
	cout<<fixed<<setprecision(2)<<x<<endl;
}

Python :

x = int( input() )
if x <= 10:
    y = 2.5
else:
    y = 2.5 +(x - 10) * 1.5

print('%.2f' % y)