159.2 or 159 1/5 If you need it as a fraction
The triangle shown is a right triangle shown by the little square inside of it.
Area of a triangle is 1/2 x height x base
Rotating the shown triangle so the square is at a bottom corner the height is 6 and the base is 6
Area = 1/2 x 6 x 6 = 18 square cm
