During the 30 days, the tank has lost 60 gallons, while Fred has added 45 gallons, so he will add 15 gallons at the end of the 30th day.
Fred is responsible for keeping the fish tanks filled at the Aquarius
Fountain Store. One of the 50-gallon tanks has a small leak and, along
with evaporation, it loses two gallons of water each day. Today the
tank is full. Fred has been instructed to add five gallons of water to
the tank at the end of every third day, and, at the end of the thirtieth
day, he will completely fill the tank, instead. How much water will
Fred add on the thirtieth day?
* Please Give Detailed Answer *