Find the inflection point of a cubic function can be found by setting $f^{\prime\prime} \left(x\right) = 0$ or $f^{\prime \prime}\left(x\right) = \text{DNE}$. What is the slope at that point?
What is the $y$-value at that point?

(show work)
$y = −12x − 70$
But your answer will probably be in point-slope form.