Assume that the tiles are 3 inches by 6 inches, although there is no reason to do that!
Area of each tile = 0.25 ft * 0.5 feet = 0.125 sq feet.
Number of tiles required = Total area to be covered/Area of each tile
= 210/0.125 = 1680 tiles.
That is the mathematical answer. In real life, the number required will depend on the configuration of the area to be tiled. For example, a circular area of 210 square feet will require far more tile cutting than a rectangular one - even fewer if both sides of the rectangle are in quarter of half feet. That then brings into play your tiling skills, wastage etc.
Tiles that are two feet on a side cover 4 square feet. 378 of them cover 1512 square feet.
76.6 tiles
67 tiles.
157 18 by 18 tiles are needed to cover 352 square feet.
You will need at least 67 tiles. This will cover 150.75 square feet.
Tiles that are two feet on a side cover 4 square feet. 378 of them cover 1512 square feet.
192 tiles
76.6 tiles
67 tiles.
190
Two tiles will suffice since they will cover 36 square feet.
Since a 12x12 tile is one square foot, then 38 12x12 tiles will cover 38 square feet.
500/1.78 = 281 tiles
start with 38 tiles.
157 18 by 18 tiles are needed to cover 352 square feet.
Each tile covers 4 square feet. You will need 24.75 tiles to cover the area.
You will need at least 67 tiles. This will cover 150.75 square feet.