A square metre is a measure of area, with two dimensions, length and width [L2]. A metre is a measure of distance, with one dimension [L]. The two measure different things and basic dimensional...
12.0
18 square meters is an area, not a length. It could be 6 meters x 3 meters.
There are about 10.8 (10.7639104) square feet in one square meter.
100 cm = 1 metre10,000 square cm = 1 square metre