Answer
$R' \text{ or } \left\{5, 6, 7, 8, 9, 10, 11, 12, 13\right\}$
Work Step by Step
$x \in U$ and $x \not \in M$ means that the elements of the given set are in U but not in R. This is actually the definition of the complement of a set R.
Thus, the given set is equivalent to:
$R' = \left\{5, 6, 7, 8, 9, 10, 11, 12, 13\right\}$
