Please help me with math.
Umm... I have no idea what that formula is, but can't you just plug in 5 for F and V and solve for E? Seems pretty simple IMO compared to some of the other problems you've posted.
5 Faces 5 Vertices Edges = ?
F + V = E + 2
E = F + V - 2 E = 8
That was so difficult
