Assume a password in a computer system contains eight character, each can be a digit (0 to 9), an uppercase english alphabet, or a lowercase english alphabet. how many password are there (a) if letters can be repeated? (b) if no letter can be repeated? (c) starts with x and letters can be repeated? (d) either starts with x or ends with 10 (letters can be repeated)? (e) neither starts with x nor ends with 10 (letters can be repeated)?