answer all parts

3. Book Section 11.1 Problem 4 (p. 747) Find a regular expression for each of the following languages over the alphabet {a,b}. a. Strings with even length b. Strings whose length is a multiple of 3 c. Strings containing the substring aba d. Strings with an odd number of a 's 4. Find a regular expression to describe the following language: {a,ac,c,ca}