P5: Triangles

The figure below shows two identical right-angled triangles overlapping each other. Find the area of the blue region. 

Solution:

The two triangles are identical,
The yellow region is overlapping and same in area or size.
Therefore, the area of the blue region is equal to the white region.
The area of the blue region =  9 × 6 + ½ × 3 × 6 = 63 cm2