#edges <= 24.
by euler's formula,
# regions/faces = e-v+2
$\sum deg(r) = 2\left | edges \right |$
if the no.of edges in the face is 3, then total no.of edges will be = $3\left | r \right |$
$\sum deg(r) \geq 3\left | r \right |$
$2\left | e \right | \geq 3\left | r \right | $
on substituting euler's formula for r,
$2\left | e \right | \geq 3\left ( e-v+2 \right )$
$e \leq 3V-6$
Substitute the given data in the above formula.
we get
$e \leq 24$