For the questions below, give a regular expression for the set of all strings of a's and b's described. 14. Strings containing only a's 15. Strings containing at most 3 a's 16. Strings with an even number of a's or exactly 2 b's 17. Strings where nob comes after an odd number of a's 18. Strings that begin with at least 2 a's, and end with no more than one b