Use the difference method to solve:

It can be observed that the area of ??the shaded part is a large triangle minus the small triangle contained in it.

The area of ??the large triangle = 1/2 the area of ??the large rectangle = 1/2*16=8

The area of ??the small triangle is also solved by using half the area of ??a certain rectangle. That is, the area of ??the small triangle = 1/2*9 = 4.5

So the final area of ??the shaded part is = the area of ??the large triangle - the area of ??the small triangle = 8-4.5=3.5