What is the area formula for a parallelogram?

Area = Length x width

It's the same as the area for a rectangle - base times height. If you think about it, a parallelogram is a rectangle with two triangles on either side - one with its base on top, one with its base on bottom. Through various identities, we know that these two triangles are congruent. So the area is the sum of the small rectangle plus the two triangles, which ends up being base times height.