Answer
a. members per year.
b. Yes, because $m'(10)$ is the number of members per year and that can be less than the last year.
Work Step by Step
a. We can see that the units are members per year by looking at the question and seeing that it is the number of members t years after founding. So, it is members per year.
b. We can see that $m'(10)$ can be negative because the number of members per year can be less than the last year.
