The question says that an additional $20,000 is spent on design and development, so the total included in part (c) is the $60,000 referred to in part (a) plus the extra $20,000 that needs to be spent. I do not know what you mean by ‘how is it added’ – 60,000 + 20,000 = 80,000 and this has been included in the answer to part (c).
I assume that you have watched the free lecture working through this example? It is in the lectures that I explain and expand on the lecture notes. If you are not watching the lectures for any reason then you must buy a Study Text from one of the ACCA approved publishers and study from there.