C :

#include <stdio.h>
void main()
{
	float x,y;
	scanf("%f",&x);
	if(x<=3)
		y=10;
	else if(x>3&&x<=5)
		y=10+(x-3)*1.8;
	else 
		y=13.6+(x-5)*2.7;
	printf("%.2f\n",y);
}

C++ :

#include<iostream>
#include<cstdio>
using namespace std;

int main()
{
	double a;
	cin>>a;
	if (a<=3.0) printf("%.2lf",10.004);
	if (a>3.0&&a<=5.0)  printf("%.2lf",10.00+((a-3.0)*1.8));
	if (a>5.0) printf("%.2lf",13.6+((a-5.0)*2.7));
	return 0;
}

Python :

# coding=utf-8
a = float(input())
if a <= 3 :
    t = 10
elif a <= 5 :
    t = 10 + (a - 3) * 1.8
else :
    t = 13.6 + (a - 5) * 2.7
print(format(t, ".2f"))