Please explain

Question 7 In a survey about time spent per week doing homework, it was found that 20% of the students spend between 0-2 hours, 30% spend between 2 and 4 hours, remaining spent more than 4 hours doing homework? If 90 students said that they spend between 2 and 4 hours, how many students spend more than 4 hours per week for homework? 150 300 450 60