Depends on how many are in each box?
start with 38 tiles.
The answer depends on the measurement units used for 18x18.
100 tiles or 96 which is the correct amount
22.2 tiles so buy 23 tiles.
18x18 what? 18 feet x 18 feet? 18 microns x 18 microns?
You'll need 200 18-inch tiles.
266.666666666 so rounding up 267 tiles.
30 tiles! But you'll need more than 30 tiles to cover wastage, breakage, etc.
The answer will depend on the units used for measuring the tiles which you have failed to specify.
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.
102.22 tiles because each tile is 2.25 sq.ft. 230 / 2.25 =102.22 so really 103 tiles.
18" x 18" = 1.5' x 1.5' = 2.25 square feet90/2.25 = 40 tiles.
To cover 720 sq feet of floor with 18" x 18" tile, you would need 320 tiles.
form_title= Carpet Tiles form_header= Cushion your feet with new carpet. Do you need to remove old flooring? What color carpet do you want to install?*= _  What is the square footage of the area?*= _ 
It depends on the number of tiles in a box!
It would take approximately 311 tiles plus 5% to 10% waste depending on how you lay your floor out and how many cuts you will have.
If the 210 square ft area is a convenient shape, or if offcuts can be used to fill up odd parts then 53 tiles will suffice.
64 tiles for a square shape of 140 square feet each tile equals 18 in x 18 in = 324 sq in 140 sq ft = 140 x (12x12) = 20160 sq in 20160 sq in : 324 sq in = 62.222 tiles sq root of 62.222 = 7.888 tiles per side so you will use 8 tiles per side and will have a leftover of .112