#### Answer

$B\cup C= \{ a,c,e,f,g \}$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To get the elements of $
B\cup C
,$ combine all the elements of $B$ and $C$.
$\bf{\text{Solution Details:}}$
The union of $B$ and $C,$ given by $B\cup C$, are the combined elements in $B$ and $C$. With $
B=\{ a,c,e,f \}
$ and $
C=\{ a,e,f,g \}
$ then
\begin{array}{l}\require{cancel}
B\cup C= \{ a,c,e,f,g \}
.\end{array}