Hi, please answer the following advanced functions question in full steps and detail. Please do not use "limits" to answer this question, Thanks! :)

With the warm weather finally here, Mrs. Smith needs to drain the old water out of her pool and refill it with clean water. The volume of water, V (litres), remaining in the pool t (minutes) after the draining has started, is: V(t) = t2 - 80t + 1600 a) Determine the average rate at which the volume of water is changing between t = 4 minutes and t = 4.5 minutes. Round your answer to 1 decimal place. Include units. b) Estimate the instantaneous rate at which the volume of water is changing at 4 minutes. Round your answer to 3 decimal places. Include units