A mold grows at a rate that is proportional to the amount present. Initially there is 5 oz of this mold, and 10 hours later there is 7 oz. When is there 15 oz of the mold? (answer in hours)

A huge inflatable raft takes 27 minutes to fill using a pump. After fully inflating, it takes 63 minutes to let all the air out of the raft. How long (in mins and seconds) would it take for the pump to fully inflate the raft while the valve was left open?    ___ munutes and ___ seconds

A large tank contains 120 gallons of pure water. Brine containing 1.5 lbs. of salt per gallon of water enters the tank at a rate of 4 gal/min. The mixture leaves the tank at a slower rate of 2 gal/min. Find an expression for the amount of salt in the tank at time t.