The complex number $$z$$ is equal to $$9+bi$$, where $$b$$ is a positive real number and $$i^{2}=-1$$. Given that the imaginary parts of $$z^{2}$$ and $$z^{3}$$ are the same, what is $$b$$ equal to?

(第二十五届AIME1 2007 第3题)