помогите решить задачку на с++

#include <iostream>
//------------------------------------------------
class PR {
  protected:
    float         *Side;
  public:
    virtual float P(void) = 0;
    PR(int N){Side = new float [N];}
    ~PR(void){
      delete [] Side;
      std::cout << "Dest!" << std::endl;
    }
};
//------------------------------------------------
class Triangle : PR {
  public:
    Triangle(float a, float b, float c) : PR(3) {
      Side[0] = a, Side[1] = b, Side[2] = c;
    }
    float P(void){
      float p = Side[0] + Side[1] + Side[2];
      std::cout << "Perimeter of Triangle = " << p << std::endl;
      return p;
    }
};
//------------------------------------------------
class Rectangle : PR {
  public:
    Rectangle(float a, float b) : PR(2){
      Side[0] = a, Side[1] = b;
    }
    float P(void){
      float p = 2.0*(Side[0] + Side[1]);
      std::cout << "Perimeter of Rectangle = " << p << std::endl;
      return p;
    }
};
//------------------------------------------------
int main() {
  PR *o;
  Triangle  *tr = new Triangle(2,4,3);
  Rectangle *re = new Rectangle(2,4);
  o = (PR*)tr;
  o->P();
  delete tr;
  o = (PR*)re;
  o->P();
  delete re;
  std::cin.get();
  return 0;
}