DIGUNDER (DEC 07 ADAPTED

Because you have written that the question was Dec 2007 (adapted) then I assume that your question is not exactly as the original exam question. Maybe your book has changed part (b) because in the original exam question, part (b) was 4 marks and was just requiring discussion of the figures calculated in part (a) with no extra complications. It is not in the current edition of the BPP Revision Kit and so I guess you have found it somewhere else. (I would not particularly worry about this question anyway. It is 15 years old and was written by a previous examiner. Although the answer you have may have corrected things, the original examiners answer to part (a) was wrong (as the current examiner has since confirmed).)