Answer:
The length of fencing will be 

Explanation:
Step 1
Find the dimensions of the rectangle
we know that
The area of a rectangle is equal to

In this problem we have

so
 -----> equation A
 -----> equation B
Substitute equation B in equation A
 

square root both sides

Find the value of b
 -----> 

step 2
Find the length of fencing
The perimeter of a rectangle is equal to

 we have


substitute
