The Hawaiian alphabet consists of letters, the vowels and the consonants and .
(a) How many different four-letter words can be constructed using the -letter alphabet?
(b) How about with the English alphabet?
(c) What is the second and last letters are vowels and the other are consonants?
(d) What if the second and last letters are vowels, but there are no restrictions on the other letters?
So for (a) it would be . For (b) it would be . For (c) it would be . And for (d) it would be ?