Do you have a protractor?
If so then measure A, B, C then add them
Area of the octagon = 8 * side length^2 / [4 * tan (180/8)]
Area of the octagon = 8 * 9^2 / [4 * tan(22.5)]
Area of the octagon = 648 / 4 * 0.41421
Area of the octagon = 648 /
<span>
<span>
<span>
1.65684
</span>
</span>
</span>
Area of the octagon =
<span>
<span>
<span>
391.1059607446
</span>
</span>
</span>
square inches
Gray Area = <span>
<span>
<span>
391.105 minus square area
</span></span></span><span>Gray Area = 391.105 -81
</span>Gray Area = <span><span>310.105
square inches
Source:
http://www.1728.org/polygon.htm
</span> </span>
The base will be 16in² and the height will be 8in²