Answer:
The number of students still need to complete their assignment is 14.
Explanation:
The total number of student is 24.
It is given that if they have completed their assignment, then they may read.
It is given that 40% of the class is reading. If means 40% of the class have complete their assignment.

The number of student can not be a faction value, therefore 10 students have complete their assignment.
The number of students still need to complete their assignment is

Therefore the number of students still need to complete their assignment is 14.