Chapter 1, Problem 1DQ

I believe the solution to the problem at this url is incorrect and that the problem requires integration. I asked this problem once before and got a very different answer (64 gallons versus 11 gallons as provided in this answer). The previous solution was much more involved but I had a hard time following the solution so I asked the question again. I would like this problem solved by a different expert please.    https://www.bartleby.com/questions-and-answers/5.-oil-flows-into-a-tank-according-to-the-rate-ft11-and-at-the-same-time-empties-out-at-the-rate-et-/cdf8b9dc-0b1c-4bfc-bb53-ad200f80692b

I need help on this question. Explain how you got your answers and why they seem reasonable.

Please help me answer these two parts to this question. My four previous answers were all marked incorrect and I'm unsure of what to do to get the correct answer. Thank you in advance!