I agree with the other poster. This response is to show why the answer is C.
The base is 12 inches. This is the horizontal component running parallel to the flat ground. The height is 3 inches which is perpendicular to the base, i.e. the two segments make a 90 degree angle. The height is completely vertical.
The area is then...
area = baseheight
area = 123
area = 36
Therefore the final answer is choice C) 36
