The answer will depend on the units used for measuring the tiles which you have failed to specify.
67 tiles.
10
288
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.
100 tiles or 96 which is the correct amount
67 tiles.
192 tiles
start with 38 tiles.
10
118
288
12...
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.
220
The answer depends on the measurement units used for 18x18.
18" x 18" = 1.5' x 1.5' = 2.25 square feet90/2.25 = 40 tiles.
22.2 tiles so buy 23 tiles.