Question: 1. Encrypt the message rubber baby buggy bumpers using a shift-by-15 cipher.
2. We will use the letters a,b,c,d,e, f to form words of length 4. No word can have two of the same letter.
(a) How many words can be made?
(b) How many words end in e f?
(c) How many words contain e f as consecutive letters?
(d) How many words contain both e and f, but not necessarily consecutively?
(e) How many words contain an e or an f (or both)?