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) All words are allowed. Your answer is : (b) No letter can be repeated in a word. Your answer is : (c) Each word must begin with the letter A and letters can be repeated. Your answer is : (d) The letter C must be at the end and letters can be repeated. Your answer is : (e) The second letter must be a vowel and letters can be repeated. Your answer is