Here we start with knowing that the area of a rectangle is the product of the lengths of two adjacent sides, that is the product of the length of the base and height: A = bh. From this we perform constructions to find the area of a parallelogram by finding the area of a rectangle with the same base and height and thus the same area. We see that a triangular region can be thought of as half of the interior of a parallelogram, leading to the formula for the area of interior of a triangle.