The number of gallons of water remaining in a tank minutes after it begins draining is given by a linear function. At minutes, there are 180 gallons remaining. At minutes, there are 120 gallons remaining. What is the rate, in gallons per minute, at which the water is draining from the tank?
6 gallons per minute
12 gallons per minute
30 gallons per minute
210 gallons per minute
