We don't see the units on the 12x12 tile, but we have to assume it's inches.
So each tile = 1 square foot.
The room measures 20-ft x 12-ft = 240 square feet.
So it takes 240 tiles to cover the ceiling, and another 240 to cover the floor.
In order to calculate how many tiles it takes to cover the walls, we need to know
the height of the ceiling above the floor.
123 will cover it. Get extras.
18ft*20ft = 360 square feet
13 boxes with 13 tiles in each
The tile is bigger than the area that you want to cover (12x12 > 10x11) so one tile will do. <><><><><> However, if you meant 12x12 INCH tiles, and a 10x11 FOOT room, you would need 110 tiles.
You would need 111 tile, but with waste you will want to get 125 tile.