Answer:
m=21 and n=21
Step-by-step explanation:
In order to maximize the area of the rectangle, you want the two side lengths to be as equal to each other as possible.
In this case, we get that 2m+2n=84, so m+n=42. In our case, m and n can equal each other, so that gives us the maximum area of 441
Proof that this works:
If we had other dimensions, like m=20 and n=22, the area would be 440, slightly less than 442. If m=19 and n=23, the area becomes 437, which is even further off from 441.
