Adam has a rectangular fish tank that measures 5 feet in length, 2 feet in width, and 3.5 feet in height. The tank is completely filled with water. It is time to clean the fish tank, and Adam decides that the best way to clean the tank is to drain the water from the tank by half. If 1 cubic foot of water is equal to about 7 gallons of water, how much water would Adam have to drain from the fish tank?
A.17.5 gallons
B.35 gallons
C.122.5 gallons
D.245 gallons