This is a net for a rectangular-based pyramid (or whatever you call it), so the triangles that are 2 apart from each other are congruent i.e. exactly the same. To find the area of a triangle, use the formula bh/2. That is, base x height ÷ 2. The base of the larger triangle (perpendicular to the height) is 19, and the height is 18.6. Plug that into the formula to get 18.6x19/2. This works out to be 176.7. The area of the rectangle is lw. That is, length x width. The length is 19 and the width is 9. 19x9 is 171. Now for the smaller triangles. The height is exactly the same as the larger one, but the base is 9, not 19. Plug that into the formula bh/2 to get 18.6x9/2. This is 83.7. Because there are two of each type of triangle, add two of them to the total. 2x83.7+2x176.7+171=691.8. There is your answer.
691.8