You Must Escape Level 3 Walkthrough: Look on the desk and pick up the hammer head.
Look under the chair and pick up the hammer handle. Tap the hammer head and handle to combine them.
Use the hammer on the emergency glass (red border) on the wall, then take the bottle of cleaner.
Look on the black thing on the right and pick up the tan cloth. Tap the bottle and the tan cloth to combine them.
You Must Escape Level 3 Walkthrough: Drag the cloth with the cleaner on the left mirror to reveal: ABXS Make sure to clean it all so your item disappears.
Go to the computer and enter the code: ABXS. You will see the code on the monitor: 8563
Enter the code 8563 on the box to open it, then take the key and use it on the door.