C :

#include <stdio.h>
int main(){
float weight;
float money;
scanf("%f",&weight);
if(weight<=10)
money=2.5;
else
money=2.5+(weight-10)*1.5;
printf("%.1f\n",money);
return 0;}

C++ :

#include<iostream>
#include<cstdio>  //standard input output
using namespace std;
int main()
{
    float w,fee;
    cin>>w;
    if (w<=10) fee=2.5;
    else
        fee=2.5+(w-10)*1.5;
    cout.precision(1);   //设置输出格式，小数点后保留1位
    cout.setf(ios::fixed);  
    cout<<fee<<endl;
    
    return 0;
}