If 4 letter words are formed using the letters A B C D E F G

If 4 -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.
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 : ( )

Solution

A-7⁴ =2401 words

B-7*6*5*4=840 words

C-1*7*7*7=343 words

D-7*7*7*1=343 words

E-7*2*7*7=686 words