2.25 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.
10
288
67 tiles.
2.25 square feet
The answer depends on the measurement units used for 18x18.
220
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.
10
288
67 tiles.
118
12...
start with 38 tiles.
18 ft X 18 ft =324 sq ft
266.666666666 so rounding up 267 tiles.