Before moving, look at the equation in the upper left corner (the countdown will not start until you move). You have ten seconds to find the missing number for each equation. Once you've got the equation right, grab the key and unlock the door. Be careful not to bump into the spiked enemies! Or worse, don't stand under the red spikes.
In later levels, the equations may not be in the correct order. When this happens, you can press the blue button which will move the listed equations down one place.
ADVICE: When you have multiple equations, you have to solve the top equation first and then go down.
Use arrow keys or WASD to move.
