So I was able to do the first part (hopefully it's right), but I'm having trouble trying to figure out what it's asking in the last parts. Here's my problem:

A business is prospering in such a way that its total (accumulated) profit after t years is $\displaystyle 1000t^2$ dollars.

a) How much did the business make during the third year?

so, $\displaystyle f(3)=1000(3)^2=9000$ hopefully its right.

b) What was its average rate of profit during the first half of the third year, between t=2 and t=2.5?

c) What was its instantaneous rate of profit at t=2?

Do I plug in the values for t in part b and c or is there something else invovled? Any help is greatly appreciated!