f5-revision-mock-exam question 27/30

Hi Mr Moffat,
firstly excellent lectures, thank you!

I did https://opentuition.com/acca/f5/f5-revision-mock-exam/ and in question 27/30
Variable costs (as % of selling price) are: product P 75%, Q 87.5%, R 60%

This percentage I did deduct from selling price,what seems to be wrong and in results calculation shows the right way is to calculate e.g. for
product P= Sales units 4800 x 25%of selling price x selling price per unit $5.
Why it is not correct to calculate contribution for product P= (Sales units 4800 x selling price per unit $5) – 75% of selling price?

Thank you,
Iki