One tile of 6 ft x 24 ft will cover 144 sq feet and so should be sufficient.
If you did not mean 6 feet x 24 feet you should have specified the measurement units that you had in mind.
Four tiles are needed.
157 18 by 18 tiles are needed to cover 352 square feet.
128.2 tiles
226 tiles
54 tiles are needed
It depends on how big the tiles are.
Four tiles are needed.
240 square tiles are needed
6' x 9' (54 square feet) = 6 square yards of tiles needed.
157 18 by 18 tiles are needed to cover 352 square feet.
128.2 tiles
226 tiles
54 tiles are needed
120
22.2 tiles so buy 23 tiles.
It would be 9 tiles wide by 12 tiles long. That gives you a total of 108 tiles.
14.4 .About 15