Answer
$$64x^3+144x^2y+108xy^2+27y^3$$
Work Step by Step
Multiplying the equation out, we find:
$$\left(4x\right)^3+3\left(4x\right)^2\cdot \:3y+3\cdot \:4x\left(3y\right)^2+\left(3y\right)^3\\ 64x^3+144x^2y+108xy^2+27y^3$$
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