SOLID [L] - Correct Implementation

solid-L-correct-implementation.cs

public abstract class Transaction
{
    public long OriginalAmount { get; set; }

    public virtual long GetTotalPaid()
    {
        return this.OriginalAmount;
    }
}

public class CreditCardTransaction : Transaction
{
    public long InterestAmount { get; set; }

    public override long GetTotalPaid()
    {
        return this.OriginalAmount + this.InterestAmount;
    }
}

public class PixTransaction : Transaction
{
}

// class that needs transacion 
public class Order
{
    // ctor and some properties

    public long TotalPaid { get; private set; }

    public void AddTransaction(Transaction transaction)
    {
        this.TotalPaid += transaction.GetTotalPaid();

        // do something more
    }
}