You can move the door's position with your mouse. You have to place the door (the one that is closer to the exit pipe) beside the exit. Then enter the first door and voila!
If you don't understand this explanation (which is possible because I'm half asleep), you can find the walkthrough here.
how to do stage 12 really donât get it pleas reply
You have to press the + key to raise the door. By the way, you can lower it by pressing the - key. I guess that's why the level is called "Addition and substraction". As fantasy4life says, think outside the box
im stuck on stage 27 "highscore board snake champion" ive gone to the leaderboards but it did nothing if im missing sometihing please let me know and fast!