With regard to the Past Year 2011 Dec Q1, the sample answer provided by ACCA, the working no.7:
Is the total cash flows supposedly equals to Opportunity cost + Additional contribution?
Yr 1: (560) + 34 = (526) Yr 2: (448) +63 = (385) Yr 3: (358) + 140 = (218), however the sample answer is (277) Yr 4: (287) + 184 = (103), however the sample answer is (240)