answer all parts please

7. Find a regular expression to describe the set of all strings over alphabet {a,b,c} which - contain at least one a 8. Find a regular expression to describe the set of all strings over alphabet {a,b,c} which - contain at least one a - and contain at least one b 9. Book Section 11.1 Problem 9 (p. 748) Find regular expressions for each of the following languages over the alphabet {a,b} such tha a. no string contains the substring aa. b. no string contains the substring aaa. c. no string contains the substring aaaa