Explain how to decompose a triangle into congruent triangles. How does the area of those decomposed triangles relate to the area of the rectangle?

So for any triangle, you can divide it into four congruent triangles by connecting the midpoints of each side. You would divide the rectangle into half, to form two congruent triangles. When you multiply the area of 1 of the triangles, it gives you the area of both triangles, and so the area of the triangle as a whole.