How to Implement class composition with inheritance in C#

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UML

C#3.5

I am new to object oriented development and appreciate your help in this regard. In my payroll system, I have four classes called ‘Payment’, ‘Salary’, ‘Earning’ and ‘Deduction’. preparing salary requires many types of earnings (like OT, Incentives, Spacial Allowance, payments for extra shifts, budgetary allowances, Brought forward amounts etc.) and deductions (like Insurance, Uniform, Loans,Recovery, Welfare, meals, salary advance taken etc.) So I split this in to two classes namely 'Earning' and 'Deduction'. Finally class 'Salary' is supposed to do the balancing part and class 'payment' will handle payment part (banking). Other type of payment is salary advance which is just an amount paid monthly. the relationships modeled, as follows… ‘Earning’ and ‘Deduction’ classes has a composition relationship with ‘Salary’ and ‘Salary’ is a derived class from ‘Payment’. I have implemented these relationships in my C# code as follows… My questions are

1.Whether I ve related classes in a proper way?

2.Is implementation of the relationships correct?

PAYMENTS

class payment
    {
        public virtual void pay()
        {

        }
}

SALARY

class salary:payment
{
//Composition of ‘Earning’ class
    private earning E1;

    public salary()
    {
        E1 = new earning(this);

    }
//Calling calEarning() of ‘Earning’ class through ‘Salary’ class
    public void calEarningForSal()
    {
        E1.calEarning();
    }

//Implementing pay method of base class 
    public override void pay()
    {

    }
}

EARNING

public class earning
   {
   //Since earning has a composition relationship with salary…
       private salary S1;

       internal earning(salary sal)
       {
           this.S1 = sal;
       }
   //This method will calculate earnings of employees
       public void calEarning()
       {

       }
   }

MAIN METHOD

Main()
        {
            salary newSal = new salary();
            newSal.calEarningForSal();
        }