Answer:
l = 10 feet, m = 30 feet and n = 25 feet
Explanation:
The attached figure shows a triangle in which three sides as as follows :
, m and 

Perimeter of triangle is 65 feet.
Perimeter = sum of all sides

put the value of n

Now put the value of l

⇒ 

And
 

Hence, l = 10 feet, m = 30 feet and n = 25 feet.