First, find the area of the triangles. So you must find the hypotenuse or the height of one triangle. So the equation will be 4 squared, + 8, squared, = c squared. You'll get 16+64=c squared. Add 16+64, which is 80, then square root that. you got 8.944, now you have the height of one triangle. Next, do
0.5*8*8.944 ("*" = multiply) then you got the area of one triangle (35.776), then just times 2, getting 71.552. Now you must find the area of the rectangle. Just multiply 8 times 20 to get 100, times 3, = 300, then add that with 71.552, the answer will be 371.552