Consider the function $f(x) = 2 x^3 - 12 x^2 - 30 x + 2$ on the interval $[ -4 , 10 ]$. Find the average or mean slope of the function on this interval.

Average slope:

By the Mean Value Theorem, we know there exists at least one value $c$ in the open interval $( -4 , 10 )$ such that $f'( c)$ is equal to this mean slope. List all values $c$ that work. If there are none, enter none .

Values of $c$: