Sep/Dec 2016 Q2 b - 75%?

Hi Sir, In this question it asks for the percentage change in selling price for NPV to equal zero. I thought I understood (and have gone back through the F9 lecture) however in the answer booklet it multiples each years revenue by 0.75 as well as the discount rate e.g. Discounted revenue cash flow = (13,250 x0.75x0.901)+(16,6695x0.75x0.812).... = £43,411,000 where does this 75% come from, I see that tax rate is 25% is it related? Thanks Max