You find a parallelogram area by this formula:
Where b is its base and h, its height.
You get b's value applying distance between two points formula.
If A and B points form the base:
And h is the perpendicular distance between both bases.
You can visit next link to know further about it:
https://www.ck12.org/geometry/Distance-Between-Parallel-Lines/lesson/Distance-Between-Parallel-Lines
-GEOM/
And in attached picture you can find an example in progress you may want to finish.
Where b is its base and h, its height.
You get b's value applying distance between two points formula.
If A and B points form the base:
And h is the perpendicular distance between both bases.
You can visit next link to know further about it:
https://www.ck12.org/geometry/Distance-Between-Parallel-Lines/lesson/Distance-Between-Parallel-Lines
-GEOM/
And in attached picture you can find an example in progress you may want to finish.