The critical points are at x = 1 and x = 4 giving you the intervals (-inf, 1), (1, 4) and (4, inf).
By substituting x values in these 3 intervals, you can see that f'(x) is positive in the first and third intervals and negative in the second interval.
This means that f(x) is increasing in the first and third intervals and decreasing in the second interval.
The answer is D.
60 minutes is 20% of 300 minutes
It is 10.7703296143, but estimated it would be about 11. Hope I helped!! :)
9 = 2(6) - b
9 = 12 - b
-3 = b
