One more time
Floor: Using one dot on the left and two dots on the right.
Left - 1
Right - 2
Right box: 19 + 2 = 21 (carry the 20 to the left as 1) = 1
Left box: 9 + 1 + 1 (carried from right box) = 11
Enter on the wall:
right box = 1 dot = 1
left box = 2 bars and 1 dot = 11