it's x ≤ 3 :))) I found it out after realizing what you were asking
I think it's $21.75 with tax
3(x-6)(x+2)
hope this helps
I'm assuming this is multiple choice and you forgot to post the answers. I'll take a guess and say it probably looks something like this:

Because you can't take the square root of a negative number without getting an imaginary result, resulting in the function having a closed domain limit.