A storage tank is in the shape of a rectangular solid; the base is a rectangle with side lengths 4 feet and 2 feet. The height of the tank is 20 feet. Initially the tank has 16 ft^3 of water. Oil is then pumped into the tank so that the rate at which oil enters the tank after t hours is 4t ft^3/hour.

(a) How much oil is in the tank after t hours? ______________ft^3

(b) What is the height of liquid in the tank after t hours? ____________ft

(c) When is the tank full? t= _______________

(d) When does the tank contain 50% water and 50% oil? t= _________________

(e) What is the average amount of liquid in the tank during the first 3 hours? average = ________________ft^3