Rectangle ABCD solution:

1) Write down everything that you know: side lengths and areas.

2) Find the width of the rectangle:

If the perimeter of the rectangle is 56 cm, and the side length of AB is 18cm and DC is 18cm, we can conclude that the lengths of AD and BC is 10cm.

3) Find the area of big triangle (ABE) in the middle (includes shaded and unshaded triangles) by using the formula A=1/2 x b x h. You are given the area of 90cm^2.

4) Subtract the area of the unshaded triangle ABF from the triangle ABE. This can be done as triangle ABF was given the area of 42cm^2.  90cm^2 - 42cm^2 = 48cm^2 for the shaded triangle.

Anna, Nithiya and Sanduni