The answer will depend on the size of the ceiling tiles!
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.
It takes 4 6x6 inch tiles to cover a square foot. You will need 180 tiles, plus some for spoilage and mistakes.
Type your answer here... You first need to make an assumption that both the tiles are square and the ceiling is square, otherwise there are any number of possible answers. Each tile would therefore measure 2 ft x 2 ft. The ceiling would be 7 tiles x 7 tiles. The width of the ceiling would be 7 tiles x 2 feet = 14 feet.
Tiles that are two feet on a side cover 4 square feet. 378 of them cover 1512 square feet.
Each tile covers 81 square inches. You have 1,296 square inches to cover. It will take 16 tiles to cover that area.
Most areas will have by-laws about covering asbestos.