You can find the area of a triangle by using this equation:
Area=(1/2)base x height
If you have the measurement for the bottom part of the sandwich, then you have your base. If you have the height of the sandwich then you have the height. Since the triangles are congruent when you find the area of one triangle, you are finding the area of the other triangle. To combine the areas of the triangles, just multiply the area of one triangle by 2.