The thickness is about 0.5cm? 20 cm wide and 30 cm long.

The volume is about 0.5*20*30=300 cubic centimeters.

The volume of the classroom:

It is 8 meters long, 6 meters wide and 4 meters high.

Volume =8*6*4= 192 cubic meters?

The volume of the classroom is about 200 cubic meters.