If 3 -letter words'' are formed using the letters A, B, C, D, E, F, G, how many such words are possible for each of the following conditions: (a) No condition is imposed.
(b) No letter can be repeated in a word.
(c) Each word must begin with the letter A and letters can be repeated.
(d) The letter C must be at the end and letters can be repeated.
(e) The second letter must be a vowel and letters can be repeated.