Defeat 100 floors level 6 you should be able to choose the key is pressed.
Press the number 3 of 6 buttons shaped like the sun's in the elevator.
Then slide or drop the plants are right next door, so the key will be visible and ready for press.
Then you can beat the 100 floors level 6 by pressing four buttons that are in the elevator and the door next to the right, see the instructions in the image above
Now continue to the 100 floors level 7 explanation, or back to the 100 floors level 5 solution