Answer
$4$
Work Step by Step
The $GCF$ of $
4
$ and $
8
$ is $
4
.$
The $GCF$ of $
x^0
$ and $
x^1
$ is $
x^0
.$
Hence, the $GCF$ of the given expressions, $
4 \text{ and } 8x
,$ is
\begin{array}{l}\require{cancel}
4x^0
\\\\=
4(1)
\\\\=
4
.\end{array}