stuck in the last part of the problem!

Now, this step is a little tricky. 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.

select name, number_grade, round(100* fraction_completed) as percent_completed from student_grades;

select name, number_grade, round(100* fraction_completed) as percent_completed,

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"
from student_grades;

Please help me with the last part of the code: " Then you can use COUNT with GROUP BY to show the number of students with each of those grades."