Suppose that we have a relation marks(ID, score) and we wish to assign
grades to students based on the score as follows: grade F if score < 40,
grade C if 40 ≤ score < 60, grade B if 60 ≤ score < 80, and grade A if 80 ≤
score. Write SQL queries to do the following:
a. Display the grade for each student, based on the marks relation.
b. Find the number of students with each grade.