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