Level 15 of the hit new iOS game 100 Floors is really easy to beat once you figure out how to read the clue.
On the door you see a series of numbers from 1 to 9 in a tic-tac-toe looking board. Over the door you see a series of four shapes. You need to match those shapes with the section of the Tic-tac-toe board that resembles the shape.
The first shape looks like a backward letter "L", like this _|
If you look at the lines of the board you see that the number 1 is surrounded by that shape, so tap "1".
The next shape looks like a capital "C", this shape is what surrounds the number 6, so tap that number.
Next up is a backwards "C" which sort of looks like this: ]
The number in that shape is a 4, tap the "4".
Finally there's an "L" shape, and the number enclosed in that shape is the "3".
So in short, tap 1, 6, 4, and 3 to open the elevator doors and continue on to the next level.
If you haven't updated the game and are still playing version 1.0, you only have 30 levels, there are 10 more free levels available when you update to version 1.1.