



 
Hi Zafar, Is this the octagon you had in mind? If so then the octagon can be partitioned into there pieces, a rectangle, which is 42 units by 21 units and hence has an area of $42 \times 21$ square units, and two congruent trapezoids. The area of a trapezoid is the average of the lengths of the parallel sides times the distance between the parallel sides. Thus in my diagram each of the pink trapezoids has area $\large \frac{42 + 30}{2} \normalsize \times d$ square units. Thus to complete the area calculation you need to know the distance $d.$ Penny  


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