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Question 2 It takes 20 hours to drain a storage tank by opening the valve at the bottom. The depth y (in metres) of fluid in the tank is related to the time t (in hours) after the valve is opened by the formula y = 1 20. (a) Find the rate dy / dt (m /h) at which the tank is draining at time t. (Marks: 5) (b) When is the fluid level in the tank falling fastest and slowest? Explain your answer. (Marks: 10) (c) Sketch y and dy / dt together and discuss the behaviour of y in relation to the signs and values of dy / dt. (Marks: 10)