The limit is equivalent to the value of the derivative of

at

. (See definition of derivative)
Answer:
Please provide a question so we can answer, thank you.
For

, we have

and so

which is, again, only valid for

.
It is m + 9 because if we let m = 60 and the lest was 9 minutes longer than m, the test would be 69 minutes long. Therefore the answer is m + 9
The answer is either to change the - 1 to 0, or to add + 1 to it next to the - 1.