In a 90-minute soccer game, Mark played 20 minutes, then rested after. He then played for another 35 minutes. How long was he on the sideline? Let's be accurate as possible.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Mark played for a total of 20 + 35 = 55 minutes. So, he was on the sideline for 90 - 55 = 35 minutes.
The answer: 35.