Henry collects rainwater for his garden. His tank.
 begins with 30 gallons of water. Over 5 days, the
 tank collects 12 more gallons of water from the
 rain. Then in 1 day, he uses 18 gallons to water
 his garden. Then over 4 days, 7 gallons
 evaporate. Then over 3 days, the tank collects
 11 more gallons from the rain.