It's prettycloseto being right! Your function is and, using the product rule and chain rule, you have

, which is correct.

But you appear to be canceling that "-1/3" with the "3" at the end of the formula. You cannot do that because they are not multiplied together. Youcancancel the "1/3" with the "3" at thebeginningof the fomula: . You can, in addition, factor out: .