Answer:
Since there are 120 chairs for 2 classrooms then you add 120 with 120 or multiply 120 with 2. for for classrooms. you will get 240 for 4 classrooms. Then for 6 classrooms, you add 240 with 120 for 6 classrooms. therefore you will get 360 chairs in 6 rooms.
120 chairs = 2 classrooms
240 chairs= 4 classrooms
360 chairs = 6 classrooms.