John has a 25-gallon fish tank. John filled his tank today with 21 gallons of water. The water
evaporates at a rate of 2.5 gallons per week. John adds 3 gallons to the tank every other week. In how
many weeks will the tank contain 8.5 gallons?
[A] 14
[B] 6
[C] 9
[D] 11