During a particular period, water enters a partially filled reservoir at a constant rate through a mountain stream. At the same time, water is pumped out of the reservoir at a constant rate through an outlet pipe. At what rate, in gallons per minute, is the amount of water in the reservoir increasing?
(1) The amount of water initially in the reservoir is 1800 gallons.
(2) Water enters the reservoir at a rate of 8 gallons per minute and is pumped out at a rate of 20 gallons every 3 minutes.