Answer:
#include<iostream>
#include<limits>
#include<iomanip>
using namespace std;
//function that returns true
//if there is invalid input like giving string as input
// for integer value.
bool isInvalidInput()
{
   //return true if cin.fail
   if(cin.fail())
   {
       //clear the buffer
       cin.clear();
       cin.ignore(numeric_limits<streamsize>::max(),'\n');
       return true;
   }
   return false;
}
//function that calculates the hire score for given 3 parameters.
double calHireScore(double agility,double strength,double speed)
{
   return (1.8*agility) + (2.16 * strength) + (3.24 * speed);
}
//calculate hire score for fox.
void calFoxHireScore()
{
   double agility,strength;
  
   cout<<"Enter Agility Value: ";
   //get agility as input and validate it.
   cin >> agility;
   if(isInvalidInput() || agility <= 0)
   {
       cout<<"\nError: Agility value must be > 0"<<endl;
       return;
   }
  
   cout<<"Enter Strength Value: ";
   cin >> strength;
   if(isInvalidInput() || strength <= 0)
   {
       cout<<"\nError: Strength value must be > 0"<<endl;
       return;
   }
  
   cout<<"\nHire Score for Fox: "<<calHireScore(agility,strength,0)<<endl;
}
//function that asks input from user for
//calculating hire score for Sloth.
void calSlothHireScore()
{
   double strength,speed;
  
   cout<<"Enter Strength Value: ";
   cin >> strength;
   if(isInvalidInput() || strength <= 0)
   {
       cout<<"\nError: Strength value must be > 0"<<endl;
       return;
   }
  
   cout<<"Enter Speed Value: ";
   cin >> speed;
   if(isInvalidInput() || speed <= 0)
   {
       cout<<"\nError: Speed value must be > 0"<<endl;
       return;
   }
  
   cout<<"\nHire Score for Sloth: "<<calHireScore(0,strength,speed)<<endl;
}
//function that asks input from user for
//calculating hire score for Bunny.
void calBunnyHireScore()
{
   double agility,speed;
  
   cout<<"Enter Agility Value: ";
   cin >> agility;
   if(isInvalidInput() || agility <= 0)
   {
       cout<<"\nError: Agility value must be > 0"<<endl;
       return;
   }
  
   cout<<"Enter Speed Value: ";
   cin >> speed;
   if(isInvalidInput() || speed <= 0)
   {
       cout<<"\nError: Speed value must be > 0"<<endl;
       return;
   }
  
   cout<<"\nHire Score for Bunny: "<<calHireScore(agility,0,speed)<<endl;
}
//function to display menu for user.
void menu()
{
   cout<<"\n1. Fox"<<endl;
   cout<<"2. Bunny"<<endl;
   cout<<"3. Sloth"<<endl;
   cout<<"0. Quit"<<endl;
   cout<<"Enter your choice: ";
}
//main method
int main()
{
   int choice;
   do
   {
       //asks choice
       menu();
       cin >> choice;
       //if invalid input print erro message
       if(isInvalidInput())
       {
           cout<<"\nError: Invalid choice enetered. Try Again\n";
       }
       else
       {
           cout<<"\n";
           //if any one of the choices do accordingly
           //for invalid choice print error mesage.
           switch(choice)
           {
               case 1:
                   calFoxHireScore();
                   break;
               case 2:
                   calBunnyHireScore();
                   break;
               case 3:
                   calSlothHireScore();
                   break;
               case 0:
                   cout<<"\nQutting...\n";
                   break;
               default:
                   cout<<"Invalid choice entered."<<endl;
                   break;
           }
       }
      
   }while(choice != 0);
  
   return 0;
}
Explanation: