If the difference between the sides of a right angled triangle is 3 cm and its area is 54 cm²; find its perimeter.

A square DEFG of side 8 cm is inscribed in a rectangle of adjacent sides 20 cm and 16 cm as shown in the figure.

The area of the shaded portion is :

1. 64 cm²

2. 128 cm²

3. 256 cm²

4. 320 cm²