SNIFF CO (DEC 07) question

Hi i have question connected with above exercise.

we are told that supervisor which is currently employed spend 10% of his working time on the hormone adding process. So if he devote 10% of his time which he normally spend on supervising standard process, why we dont add lost contribution on standard product and cost of 10% extra time to incremental cost of new project(perfumes with hormone). i understand that 35,000 is sunk cost because company incurr it even if not undertake project, but extra 10% of time would not be incurred if we do not add hormones.

thank you in advance for clear my confusion