So this is pretty simple. What you have to do is calculate the area of both triangles and subtract the two.
The formula for the area of a triangle being [tex] \frac{bh}{2} [/tex]
15 * 15 = 225.
225/2 = 112.5
26 * 27 = 702.
702/2 = 351
351 - 112.5 = 238.5
238.5 being the answer.
