Need queries in mysql.

In question 13, the average actually means the total number of students with D or F/total number of enrolled students.

Given the following tables: o students(sid,name,age,gpa) e courses(cid,deptid, name) . professors(ssn,name,address,phone,deptid) * enrollment (sid.cid,section,grade, foreign key (sid) references students, foreign key (cid) references courses foreign key (cid,section) references teaches) . teaches(cid,section,ssn, foreign key (cid) references courses foreign key (ssn) references professors) Domain . cid is in {'198:11',640:151','198:112'....] . deptid is in 'cs','math'music,.. . grade is in ['A','B','('... section, age, ssn are an integers . address, phone, name are strings . gpa is float