Mark M. answered 12/10/22
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
The absolute extrema of a continuous function that is defined on a closed interval occur either at a critical number in the interval or at an endpoint.
f'(x) = 14x - 42 = 0 when x = 3
Check f(3), f(4), and f(-4). The largest of these three values is the absolute max and the smallest is the absolute min.