For this you have a rectangle and a half circle:
Area of a rectangle = Length * Width
Area of a Half Circle = .5 * pi * r(squared)
Length = 20
Width = 16
r = 8
Since 16 is the diameter of the circle we cut it in half for the radius:
[tex]rectangle = 16 \times 20 = 320[/tex]
[tex]half \: circle = .5 \times \pi \times {r}^{2} [/tex]
[tex].5 \times \pi \times {8}^{2} = 100.53[/tex]
Add the results and you get:
420.53