3. (8 marks) Suppose that when a patient takes a blood thinner drug, the amount of drug (in mg) in the patient's blood can be modelled by: A(t) = or\" where time t > 0 is measured in hoursI and where k is some positive constant. (a) Find all critical point(s) of the function A (where t > D) and determine if they are local maximum(s) or minimum(s). Remember to find both t- and Avalues (i.e. both coordinates of the point). You should answer with exact values. and your answers might depend on k