We consider the function when moving from left to right. So the first part, from x = -∞ to -2, is decreasing. The next part from -2 to 3 (exclusive) is constant. The last part, from 3 to ∞, is increasing.
(a)
Answer: A. The increasing interval is [3, ∞).
The bracket means 3 is included in the interval, closed on that side. It's open on the infinity side; infinity itself isn't really a number so not included in the range.
I'll guess the rest is:
(b)
Constant on the interval (-2,3).
That interval is open on both ends, so doesn't include -2 or 3.
(c)
Decreasing on the interval (-∞, -2].
