Answer
$-\frac{558}{81}$.
Work Step by Step
Since $ f(x)=\frac{12}{x}-x^3$, then we get
$$ f'(x)=-\frac{12}{x^2}-3x^2, \quad f''(x)=\frac{24}{x^3}-6x, \quad f'''(x)=-\frac{72}{x^4}-6.$$
Hence, $ f'''(-3)=-\frac{72}{81}-6=-\frac{558}{81}$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.