3. The volume, V (in Litres), of liquid in a storage tank after 1' minutes is described by the equation V(t) = 250(40 t)2, o s t s 40. [6] a) What volume of liquid is stored in the tank initially? b) What is the average rate of change of the volume during the rst 20 minutes? c) What is the instantaneous rate of change at 20 minutes? Solve using limits. (Hint: Expand and simplify rst.)