The area of a square porion(red shaded) is,
[tex]A_1=21\times12=252ft^2[/tex]
Area of the black shaded portion,
[tex]\begin{gathered} A_2=(16-12)\times(21-16.5) \\ =18ft^2 \end{gathered}[/tex]
Since 21-16.5=4.5 ft, the areaof the green shaded portion is,
[tex]\begin{gathered} A_3=13.5\times(19.5-4.5) \\ =202.5ft^2 \end{gathered}[/tex]
