(2/3х-3у) в кубе помогите

(2/3х -3у)^3=(2/3х)^3-3*(2/3х)^2*3у+3*(2/3х)*9у^2-27у^3 =8/27х^3-4/х^2+18у^2/х-27у^3=(8-108х+216х^3у^2-729х^3у^3)/27х^3