Swap it for an excerpt from current assignment (MT365):-
Explain why it is not possible to have a semi-regular polyhedron in which
exactly three faces, namely a triangle, a square and an octagon, meet at
each vertex. (It is not sufficient merely to observe that such a polyhedron
is not in the list on page 35 of the unit.)
(Please, no-one post the answer as I haven't submitted mine yet. I'm not looking for other people to do my assignment)