Please show all your working and explain as best as you can

3. (12 points, 6 points each) Give a recursive definition for the following sets: a. The set S of ordered pairs (m, n) where m and n are positive integers and m is divisible by 3 and n is divisible by 7. b. The set S of strings on the alphabet A = {a, b, c} that start with a and have an odd number of characters