Answer
$\color{blue}{C \cup E = \left\{1, 3, 5, 7\right\}=E}$
Work Step by Step
Given:
$C=\left\{1, 3, 5, 7\right\}$
$E=\left\{3, 7\right\}$
RECALL:
$C \cup E$, the union of sets C and E, is the set that contains the combined elements of sets C and E.
Thus,
$\color{blue}{C \cup E = \left\{1, 3, 5, 7\right\}=E}$
