WEBASSIGNCALCLT$22\mathrm{.}1\mathrm{.}002$C$.$

$($a$)$ Find a formula for the slope $m$ of the tangent line to $f(x)=14x-x^3$ at any point $x=a.$

$m(a)=$

$$

$($b$)$ Find the slope of the tangent line to $f(x)$ at $x=-1$ and $x=2.$

$m(-1)=$

$$

$m(2)=$

$$

$$