(b) How many bit strings of length 6 or less are there? (Count the empty string of length zero also.)
(c) How many strings of 5 lower case English letters are there that have the letter x in them somewhere? Here strings may use the same letter more than once. (Hint: It might be easier to first count the strings that don't have an x in them.)
(d) A particular brand of shirt comes in colors, has a male version and a female version, and comes in sizes for each sex. How many different types of this shirt are made?
You can earn partial credit on this problem.