My question is on #9. I GOT THE ANSWER which is:

384t^2 + 73.6t - 8.64

and

5.935473877 hours

but my question is WHY I use the composite function in order to answer that question.

The question asks for time from a function N that measures number of bacteria. However, in N(T(t)) T(t) is temperature and not time.

Can someone please explain this to me?

Any help would be greatly appreciated!

Thanks in advance!