#### Answer

$A\cap B= \{ a,c \}$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To get the elements of $
A\cap B
,$ get all the common elements of $A$ and $B$.
$\bf{\text{Solution Details:}}$
The intersection of $A$ and $B,$ given by $A\cap B$, are all the common elements of $A$ and $B$. With $
A=\{ a,b,c,d \}
$ and $
B=\{ a,c,e,f \}
$ then
\begin{array}{l}\require{cancel}
A\cap B= \{ a,c \}
.\end{array}