[SOLVED] Permutation and Organized Counting

hey guys can any1 help with this question its really confusing.

A Canadian postal code uses six characters. The first, third, and fifth are letters, while the second, fourth, and sixth are digits. A U.S zip code contains all 5 characters, all digits.

a) How many codes are possible for each country?

b) How many more possible codes does the one country have than the other?

the answer for

a) Canada : 17 576 000

U.S : 100 000

b) 17 476 000

any idea how you get that answer?