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Let $f$ be the function defined by $f(x)=e^{3x},$ and let $g$ be the function defined by $g(x)=x^3.$ At what value of $x$ do the graphs of $f$ and $g$ have parallel tangent lines?

$-0\mathrm{.}261$

$-0\mathrm{.}526$

$-0\mathrm{.}484$

$-0\mathrm{.}657$

$-0\mathrm{.}344$