I need help with this two quieries.

here is the relational tables

students(sid,name,age,gpa) // sid is the primary key

courses(cid,deptid, description) // cid,deptid is the primary key

professors(ssn,name,address,phone,deptid) // ssn is the primary key

enrollment(sid,cid,section,grade) cid makes reference to the courses table. // sid, cid, and section is the primary key

teaches(cid,section,ssn). cid, section makes reference to the enrollment table // cid, section is the primary key

I need help with these 2 quieries.

a. List ssn and name of professors that work for the cs department, but are not teaching any cs courses.

b. List the number of courses offered by each department. Just the number of courses (not sections).