Answer:
 B)  maximum at 15
Step-by-step explanation:
Factor the leading coefficient from the first two terms.
 -(x^2 +6x) +6
Add the square of half the x-coefficient inside parentheses and subtract the same quantity outside.
 -(x^2 +6x +9) +6 -(-9)
 -(x +3)^2 +15
Compared to the form
 a(x -h)^2 +k
we find a=-1, h=-3, k=15. The negative vertical scale factor (a=-1) means the parabola opens downward. The vertex is located at (h, k) = (-3, 15).
The maximum value is 15.
