Find the surface area of this figure

First you would find the area of the side triangles using the area formula of a triangle which is (1/2)bh or in this case (1/2)(16)(20) and you get 160. Next, you would multiply that by five because there is 5 side triangles and you get 800. Last you would add it to the bottom area (440.4) and you would get the answer of 1240.4 mm^2