Can't complete SQL UNIT 2, Lesson 3 - Code seems right, Khan Academy autograder will not accept answer

TOTAL NEWBIE, No coding background at all. Trying to learn SQL basics.

Course Material:
The goal is a table that shows how many students have earned which letter_grade. You can output the letter_grade by using CASE with the number_grade column, outputting 'A' for grades > 90, 'B' for grades > 80, 'C' for grades > 70, and 'F' otherwise. Then you can use COUNT with GROUP BY to show the number of students with each of those grades.

CREATE TABLE student_grades ( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, number_grade INTEGER, fraction_completed REAL); INSERT INTO student_grades (name, number_grade, fraction_completed) VALUES ("Winston", 90, 0.805); INSERT INTO student_grades (name, number_grade, fraction_completed) VALUES ("Winnefer", 95, 0.901); INSERT INTO student_grades (name, number_grade, fraction_completed) VALUES ("Winsteen", 85, 0.906); INSERT INTO student_grades (name, number_grade, fraction_completed) VALUES ("Wincifer", 66, 0.7054); INSERT INTO student_grades (name, number_grade, fraction_completed) VALUES ("Winster", 76, 0.5013); INSERT INTO student_grades (name, number_grade, fraction_completed) VALUES ("Winstonia", 82, 0.9045);

MY CODE:
SELECT
  CASE
    WHEN number_grade > 90 THEN 'A'
    WHEN number_grade > 80 THEN 'B'
    WHEN number_grade > 70 THEN 'C'
    ELSE 'F'
  END AS letter_grade,
  COUNT(*) AS count
FROM student_grades
GROUP BY letter_grade
ORDER BY letter_grade;