Its 9 because it includes f(x)
There are 12 boys enrolled in algebra 2
Answer:

What is given to you is interval notation. We have the interval start at 0 and end at 8. The value 0 is not included in the interval as indicated by the parenthesis. So we go with a "less than" sign (instead of a "less than or equal to" sign)
The value 8 is included since a square bracket is used here. The use of "or equal to" is needed to make sure the endpoint 8 is included.
So x can be any number between 0 and 8. It can't be 0 but it can be 8.
We need to expand the square binomial and then multiply:
<span>3x(x + 3)^2
= 3x(x + 3)</span>(x + 3<span>)
= 3x(x^2 + 6x + 9)
= 3x^3 + 18x^2 + 27x</span>