M263: Unit 14 - Brick Wall!!!

Well it's finally happened. I just don't get unit 14. I have tried working my way through questions 4, 5 and 6, by following examples in the course text and get about halfway through answering the question when bang I hit a brick wall. It looks like I will for the first time ever not be sending in a complete TMA. What is doubly frustrating is this is the first section in any course text for any course that I have not fully comprehended.