If you think about it, an octagon is made up of 8 triangles. So you first find the area of one triangle then multiply it by 8 for the total area:
A=1/2bh
A=1/2(9.9)(12)
A=59.4
59.4 x 8= 475.2
Therefore the total area for the octagon should be 475.2 units^2
Hope this helps !
