Given:
Rectangular room is 10 feet; and
1 x 1 ft tiles
The expression for this problem would be:
If we know that the width is w, while the length is w + 10, therefore the perimeter is 2w + 2 (w + 10), so you need 4w + 20 - 4, or 4w + 16 tiles. Since you do not want to count the corners, twice.