How many students are enrolled in "English"?
select count(*) from courses as t1 join student_course_enrolment as t2 on t1.course_id = t2.course_id where t1.course_name = "English"
So what is the name of the course that has the least student enrollment?
select t1.course_name from courses as t1 join student_course_enrolment as t2 on t1.course_id = t2.course_id group by t1.course_name order by count(*) asc limit 1
How about the course that has the most student enrollment?
select t1.course_name from courses as t1 join student_course_enrolment as t2 on t1.course_id = t2.course_id group by t1.course_name order by count(*) desc limit 1