You are given the dimensions of the whole triangle, along with the dimensions of the non shaded triangle.
The shaded part is the whole triangle minus the white triangle. Because if you put the red and white together, it makes the whole triangle.
The whole triangle has an area of 36cm^2:
(6+3)•(6+2)=9•8=72
72/2=36
The white triangle has an area of 9:
3•6=18
18/2=9cm^2
The red and white parts put together make the whole shape, so if you take away the white from the whole, you get the red.
36-9=27cm^2
So the area is 27cm^2
Hope this helps!!