We'll start by adding the methods to the repository interface:

public interface IDataRepository
{
  ...
  QuestionGetSingleResponse 
    PostQuestion(QuestionPostRequest question);

  QuestionGetSingleResponse 
    PutQuestion(int questionId, QuestionPutRequest question);

  void DeleteQuestion(int questionId);

  AnswerGetResponse PostAnswer(AnswerPostRequest answer);
}

So, we are required to implement methods to add, change, and delete questions as well as adding an answer.