Consider the function $f(x) = \frac {1} {x}$ on the interval $[ 2 , 10 ]$.
(A) Find the average or mean slope of the function on this interval.

Average Slope =
(B) By the Mean Value Theorem, we know there exists a $c$ in the open interval $( 2 , 10 )$ such that $f'( c)$ is equal to this mean slope. Find all values of $c$ that work and list them (separated by commas) in the box below.

List of values: