A tank has a hole in the bottom of it so that water drains out of the tank at a constant rate of 1.5 gallons per hour. When there are 25 gallons of water left in the tank, water begins flowing into the tank from a hose at a constant rate of 3.5 gallons per hour.
Write a formula that expresses the number of gallons of water in the tank, v, in terms of the number of hours t since water began flowing into the tank