1. The problem statement, all variables and given/known data If a tank holds 5,000 gallons of water which drains from the bottom of the tank in 40 minutes, then Torricelli's Law gives the volume V of water reminaing in the tank after t minutes as V = 5000(1 - t / 40)2, 0 <= t <= 40. The rate at which water is draining from the tank after 10 minutes, in gal/min, is 2. Relevant equations 3. The attempt at a solution I figure I'll just find f'(t). [5000 lim h-> 0 (1 - (t+h)/40)2] - [5000 lim h->0 (1 - t/40)2] But now I'm stuck. I believe I have to use the power rule but don't see how to implement it.