Case 2: Each face is a square. Now we have \(e = 4f/2 = 2f\text{.}\) Using Euler's formula we get \(v = 2 + f\text{,}\) and counting edges using the degree \(k\) of each vertex gives us
\begin{equation*}
e = 2f = \frac{k(2+f)}{2}\text{.}
\end{equation*}