I have derived a formula for the generating function as 2/3x^{3}/ 1-1/3x^{3}and am asked to manipulate this so that it follows the general formula for a distribution (Geo/Poisson/Bi/Negative Bi/Uniform)

I have a feeling that it is a negative binomial distribution, since 2/3x^{3}= (0.8736x)^{3}but I dont know how to rewrite the denominator in the form of (1-ax)^{3}

If I can do that, then I can rewite the whole thing as (0.8736x/1-ax)^{3}which is a general negative binomial with r=3, p=0.8736 and q=a right?