There are 2 "air ducts", one from which you came into the room, and one that's slanted. You have to climb up the slanted one by scaling down. picking up a box, scaling up. With the now bigger box, block the path of the unmovable boxes by putting the bigger box before the shoot at which the unmovable boxes fall down. That way you make a staircase leading you to the slanted air duct. Than just follow the path and you'll get back to the yellow door.
I wanted to add hints, but there wasn't enough time. If you revisit the game, I hope this helps.
