How to solve for n using my knowledge of permutations
NP5=18N-2P4N!/(N-5)!=18(N-2)!/(N-6)!(N(N-1)(N-2)!)/(N-5)(N-6)!=18(N-2)!/(N-6)!N(N-1)/N-5=18N^2-N=18N-90N^2-19N-90=0N=9,N=-10-10 is not possible so N=9