You can put this solution on YOUR website!
Do you know the quadratic formula?
It appears that you do.
your sqr_root(180) reduces to 6sqr_root(5) by the way
so now you have:
pull/factor a 6 out of the numerator
6/18 reduces to 1/3
so the final answer i'm coming up with and you seem to already have is:
I appears as if the answer key is incorrect
Your answer appears correct but make sure you simplify like I pointed out
I hope that was helpful
Let me know if you are still confused