First equation gives the input RATE.....second equation gives the output RATE
first equation - second equation = net input rate (like how much is filling the tub)
(3) will tell you the NET RATE of tank filling at 3 hr
3(3^2)+2 - (4(3)-1 )=
29 - 11 = 18 After 3 hours THE FILLING RATE is 18 gallons/hr