database relational algebra question

Consider the following schema: ExtraCurriculum (Course_code, school, title, description) Enrolls_in (Course_code, StudentID) Student (StudentID, DOB, name, address, phone_no) a) Use Relational Algebra to find students who are either enrolled in ‘pottery classes’ or ‘self-defence classes’ using UNION. b) Use Relational Algebra to find students who are not enrolled in any extra curriculum courses. c) Use SQL to list the students in alphabetical order who are enrolled in more than 3 different kinds of extra curriculum courses.