Chapter 1 Lecture example 1 "Agne and Dace"

Hello dear tutor and thank you for the nice lecture!
What I cannot understand is the time apportion of 4000 post acq profit.
I thought that it’s enough to do the following in order to achieve post acq profit:
24000*10/12 =20 000, therefore 24 000 – 20 000= 4 000.
Why do one need too do: 4 000*10/12 and 4 000*2/12?
I was also thinking about that fact that is not mentioned in the question the the profit accrues evenly and that might be the reason but I am confused.

Thank you!!!