Hello and welcome to web2.0calc :)))
(n)(n-1)(n-2)/3/2 is how many points of 3 you can select from n points (or number of triangles)
(n)(n-1)(n-2)(n-3)(n-4)(n-5)/6/5/4/3/2 is how many points of 6 you can choose from n points (number of hexagons)
(n)(n-1)(n-2)/3/2 = (n)(n-1)(n-2)(n-3)(n-4)(n-5)/6/5/4/3/2
1 = (n-3)(n-4)(n-5)/6/5/4
120 = (n-3)(n-4)(n-5)
n = 9
=^._.^=