Make the bottom number the same to find the increase
find the increase from 1/2 to 7/10 1/2 times 5/5=5/10 from 5/10 to 7/10 is 2/10 or 1/5 increase 3 gallons was added so 3 gallons=1/5 of the container times 5/1 both sides 15 gallons=5/5 of the container