What is the area of the envelope (including the stamp area) ?

The area of the envelope is in.^{2}.

Solution:

Area of rectangle = base × height

= 16 in. × 9 in.

= 144 in.^{2}.

=

= 40 in.^{2}

Area of the envelope = Area of rectangle + Area of triangle ABE

= 144
in.^{2} + 40 in.^{2}

The area of the envelope is 184 in.^{2}