A water tank drains at a constant rate. It contains 930 liters of water 3.5 minutes after it started to drain. It takes 50 minutes for the tank to empty. Let W be the amount of water in the tank (in liters) t minutes after it started to drain.
a) find a model for W(t), the amount of water in the tank at any time after it started to drain. Write down the rate at which the water tank is emptying.
b) write down the rate at which the water tank is emptying.
c) use your model to find the amount of water in the tank after 30 minutes.