Answer:
x = -2
Step-by-step explanation:
From x = -2 to x = 5, f' is negative. That means f is decreasing.
From x = 5 to x = 6, f' is positive. That means f is increasing.
The negative area (between x = -2 and x = 5) is larger than the positive area area (between x = 5 and x = 6). That means f decreases more than it increases.
So f is an absolute maximum at x = -2.