Bpp revision kit question 164

Hello

I was solving the question 164 (a), and on the anwers it shows that the fixed costs of Machine of $4000 and $6000 respectively were added to calculate the cost of making the two products in-house in order to be compared against buying those units.

Im confused as to why are those costs added while the question says they are fixed costs and so they will be incurred even if those units are not made.