concept of base, derive class and use them properly

you have to use the concept of base, derive class and use them properly. while doing it, I'm faced with some problems. Can you help me solve the issues ?

My Code :

#include <iostream>


class Base {
    public:
    Base (int data) : _data(data){}
    virtual void printData(){
        std::cout << "Base" << _data << std::endl;
    }

private:
    int _data;
};

class Derived : public Base {
    public:
    Derived(derivdata) : Base(derivdata){}
    void printData(){
        cout << "Derived " << _data << endl;
    }
}


int main(){
    Derived *var = new Derived(5);
    var-> printData();
    Base *basevar = static_cast<Base>(*var);
    basevar-> printData();
}