Answer
Area of the shaded part = 54 ft$^{2}$
Work Step by Step
To find the area of the shaded portion we simply find the area of the entire triangle and subtract the area of the un-shaded square.
Area of a Square: $A$$_{sqr}$ = $s$$^{2}$
Therefore:
$A$$_{sqr}$ = (3 ft)$^{2}$
$A$$_{sqr}$ = 9 ft$^{2}$
Area of a Triangle: $A$$_{tri}$ = $\frac{1}{2}$$b$$h$
Therefore:
$A$$_{tri}$ = $\frac{1}{2}$(18 ft)(7 ft)
$A$$_{tri}$ = 63 ft$^{2}$
$A$$_{total}$ = $A$$_{tri}$ - $A$$_{sqr}$
Therefore:
$A$$_{total}$ = 63 ft$^{2}$ - 9 ft$^{2}$
= 54 ft$^{2}$
