Total number of students = 150.
Total number of books by all students = b books.
Average of number of books each student donated = (Total number of books denotend by all students) ÷ (Total number of students).
= b÷150 books by each student or b/150.
Hannah donated 3 times as many as the average number of books each student donated.
3 times of Average of number of books each student donated = 3 * b/150
= b/50.
Therefore, the expression for number of books Hannah donate = b/50
