(i)[3]
the vowels $(A, E, O)$ are grouped together and the consonants $(C, G, H, N, P)$ are grouped together.
(ii)[4]
the Es are not adjacent to one another.
(iii)[5]
Four letters are chosen from the $10$ letters of the word COPENHAGEN. Determine the number of different selections if the four letters are required to have the same number of Es and Ns, with at least one of each.