First thing first your gonna have to find the area of the triangle within the rectangle.
Area of triangle = 1/2 b x h
= (1/2 9) x 4
= 4.5 x 4
= 18 cm square
Then after finding the area of the triangle your gonna find the area of the rectangle.
Area of rectangle = length x width
12 x 4 = 48
= 48 cm square
Then your gonna subtract the area of the triangle from the area of the rectangle.
Area of rectangle = 48 cm square
Area of triangle = 18 cm square
= 30 cm square
So the shaded region is 30 cm square
