Answer
$$m^2-n^2$$
Work Step by Step
We use the equation for the area of a parallelogram to find:
$$A=bh \\ A=\left(m+n\right)\left(m-n\right) \\ A=m^2-n^2$$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.