How can i write the sql query for this question below? : Among the students registered for the course "Psychology". what % of them have a GPA > 3?

Student:  
student_id* | student_name | student_gender

Course:  
course_id* | course_name | course_type 

Student_course_grade:  
student_id | course_id | grade

Please note : 
1. Grade field in Student_course_grade table is a number in (5,4,3,2,1)  instead of a letter grade like (A,B,C,D,E)
2. For a student who has registered for a course and has not completed it yet, the grade will be null.
3. GPA= Grade Point Average ( average of all grades scored by the student)