My problem comes from the Further Pure Maths 2 textbook from AQA (UK exam board - A-Level).

Page 28 of the textbook: http://filestore.aqa.org.uk/subjects...2-TEXTBOOK.PDF

Here's the question in the texbook:

Now I'm confused by the workings out of question (b), specifically on the first line where it says . I would have though it would have been just . Could someone explain to me why the 4 is multiplied by 3? I understand everything else but this does not make sense to me.

Here is some background information on the previous page (page 27 in the textbook):