2.25 square feet
4,800 6-inch square tiles.
It is not clear what is meant by an "18x18 square feet" tile. 18ft * 18 ft = 324 square feet, so that one tile will be more than enough. An 18 inch by 18 inch tile cannot be a 18x18 square feet tile.
67.5
440 6-inch square tiles.
1.78 sq feet per tile.
A square 20-inch tile is 2.78 square feet.
3.5555 square feet.
2.25 square feet
This tile has an area of 1 ft2.
1.78 square feet.
4,800 6-inch square tiles.
There are 144 18 square inch tiles in an area of 18 square feet.
It is not clear what is meant by an "18x18 square feet" tile. 18ft * 18 ft = 324 square feet, so that one tile will be more than enough. An 18 inch by 18 inch tile cannot be a 18x18 square feet tile.
1.78 square feet.
67.5
Approximately 96 square feet.