There are a number of methods of finding triangle area from coordinates. In this case, it is simplest to use the formula
... A = (1/2)bh
where b is the base length and h is the height.
Since one side of the triangle is parallel to one of the axes, it is convenient to use that as the base. Its length is 8-2 = 6. Then the height is the distance from the remaining point to that line, a distance of 4.
... A = (1/2)(6)(4) = 12
The appropriate choice is ...
... (C) 12 square units