For part b) of this question,, the labeling of sales mix variance values as favourable or adverse given at the back of the book is 9442 favourable, 7560 adverse and 11484 adverse which seems to be wrong..
I assume you are referring to the answer in the BPP Revision Kit, in which case the labelling is wrong. The variances should be 9,442 (A), 7,560 (F), and 11,484 (A). The total (which is all that matters) is correct as 13,366 (A).
Although you can set out your workings for the 13,366 (A) in several ways (and which way does not matter), I don’t like the way BPP have shown it. I find it more logical to do it the way I show in my free lectures (which is actually the way the examiners own answer does it for this question).