solution

#include<iostream.h>
#include<conio.h>

int main()
{
 int calls;
 float bill;
 cout<<"Enter number of calls : ";
 cin>>calls;

 if(calls<=100)
  bill=200;
 else if (calls>100 && calls<=150)
   {
       calls=calls-100;
       bill=200+(0.60*calls);
 }
 else if (calls>150 && calls<=200)
 {
  calls=calls-150;
  bill=200+(0.60*50)+(0.50*calls);
  }
 else
 {
  calls=calls-200;
  bill=200+(0.60*50)+(0.50*50)+(0.40*calls);
 }

 cout<<" Your bill is Rs."<<bill;

 getch();
 return 0;
}