Answer
$m^n$ elements
Work Step by Step
The Cartesian product $A^n$ means A x A x A x A... n times.
And we know that when A has m elements, A x A would have $m x m = m^2$ elements.
So A x A x A x A .... n times would have $ m x m x m x m ....$ n times $= m^n$ .
