not 100% sure its been a while. but ill try to explain.
so for the box on the top the sides are 10 and 8. the squares area is 80.
or the triangles, the height is 3 inches and base is 8 inches. so 8x3 is 24. but for triangles you divide by two. so it would be 12 for one triangle resulting in 24 for both of them.
now lets combine the bottom two boxes. each side is 10 because 10 on one side and 5+5 is 10. so 10x10=100.
if we take all the values and add them up well get 204.(80+24+100=204.
have a good day