So it is 12 x 31 which equal ls 372.
No. It's 12 feet by 31 feet, which equals 372 square feet. The units make a huge difference!
Since the tiles are 12 by 12 inches squared
No. They're 12 inches by 12 inches, for 144 square inches; or 1 foot by 1 foot, for 1 square foot. The units are necessary to make sense of the numbers you get!
with 25 in a box
The exercise as originally posted doesn't say anything about boxes. It asks for how many tiles. Are you supposed to be finding tiles, or boxes? If boxes, what does the original exercise really say?
you 372/25 = 14.88 So you would need 15 boxes.
If the exercise asks about boxes instead of tiles then, yes, you'd need to round up to fifteen boxes.