Let $x,$ $y,$ $z$ be positive real number such that $xyz = \frac{2}{3}.$  Compute the minimum value of
\[x^2 + 6xy + 18y^2 + 12yz + 4z^2.\]
Question:
Let $x,$ $y,$ $z$ be positive real number such that $xyz = \frac{2}{3}.$  Compute the minimum value of
\[x^2 + 6xy + 18y^2 + 12yz + 4z^2.\]
Answer:
Let's think step by step.

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18
Let $x,$ $y,$ $z$ be positive real number such that $xyz = \frac{2}{3}.$  Compute the minimum value of
\[x^2 + 6xy + 18y^2 + 12yz + 4z^2.\]
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