The area of the triangle extension is 12, because the total side length it is on is 18, and the segments to the sides of the triangle are 6 each, meaning 18-12=6, the height of the triangle. The base is given as 4, so 1/2(4x6)=24/2=12.
Add this to the area of the rectangle, 9x18=162, and 162+12=174.
