Use the key to open the gray box on the wall.
Open the yellow box and take the ball.
Open the toilet and take the ball.
Tap the corner of the carpet next to the toilet to lift it, then take the ball.
Place all 4 balls into the gray box and the door will unlock.
Proceed to the next 100 Toilets level!
Hit like if the 100 Toilets Level 37 walkthrough helped you! Thanks :)