Need help with a maximum revenue problem

Find the number of units x that produces a maximum revenue R if R = 30x^2/3-2x.

IF I'm right, the first derivative is 2/3(30x)^(-1/3)-2, and the second derivative is -2/9(30x)^-4/3.

This is where I run into the issues because I'm not good at all at figuring out which of the numbers in the exponent is supposed to go to the denominator and also what root it's supposed to be. I haven't taken any math classes for nearly 8 years and then I jumped right into Survey of Calculus, which is essentially calculus for business, and I'm having a great deal of difficulty. I need assistance with this question as it's on a quiz that's due tomorrow so if any of you could offer some assistance I would greatly appreciate it!