Devon studied the composite figure. A rectangular prism with length of 20, width of 34, and height of 9. A triangular prism with triangular sides with a base of 20 and height of 24. The rectangular sides have a length of 34 and height of 26. He believed the surface area, in square units, could be found by simplifying the expression 2 ((9) (20)) + 2 ((9) (34)) + (34) (20) + 2 (one-half (20) (24)) + 2 (one-half (34) (26)). What error did Devon make? He used 26 instead of 24 as the slant height of one set of lateral faces. He omitted the rectangle where the upper and lower solids join together. He included the 34 by 20 base of the figure. He believed the upper part of the figure was a pyramid instead of a prism.