Use cardboard and construct a parallelogram with base (b) and height (h) as shown in the figure.
As shown in the figure, fold the cardboard perpendicularly from the bottom right vertex and cut folded part.
Now, bring the cut part (triangle) to the left and join as shown the given figure. What shape do you get?
Here, the rectangle has length (b) and breadth (h).
Hence the,
Area of rectangle = length × breadth = b × h
Here,
Area of rectangle = area of parallelogram.