To find the area of the shaded region, you can split it up into simpler shapes, like a rectangle and trapezoid, or even further into two rectangles and a triangle (see attachment).
The total area of the shaded region is then
\(\dfrac12\times3\times10+10\times1+8\times2=15+10+16=41\text{ ft}^2\)
The total area of the entire rectangle is \(16\times8=128\text{ ft}^2\), which means the area of the unshaded region is
\(128-41=87\text{ ft}^2\)
