Question: Determine a simplified expression of the shaded area in terms of a and b?

If (5a+b) is the whole length of one side, that means length of the shaded rectangle would be (5a+b-a-a). That equation simplified is (3a+b). Same thing for the height. If it’s (3a-b), that means that the height of the shaded rectangle is (3a-b-a-a) which simplifies to (a-b). Multiply (3a+b) with (a-b) and it gives you the area of the shaded rectangle which is 3a^2-2a-b^2.