Final answer:
The correct expression for the total number of points earned by the class is 10n - 40, accounting for all but four students not completing their homework.
Step-by-step explanation:
The expression for the total number of points earned by the class is 10n - 40. This is derived by first assigning n to represent the total number of students in the class. Since each student earns 10 points for their homework, the total points for all students is 10n. However, as 4 students did not do their homework, their potential points are not included in the total. Thus, we subtract 40 points (which is 10 points for each of the 4 students) from the total, resulting in the expression 10n - 40.