If there are x, five, y, six and z sides, then there are 2/3z vertices, then 5x+6y = 2z, and there is an Euler formula, that is, the relationship between faces, points and edges. I forgot, too, so I won't study this year. I can't help it if I'm wrong ... By the way, xyz is an integer, so I have to work out the answer ... If I can't figure it out, I'll take one.