The area of the garden is the product of its dimensions
- The dimension that maximizes the area is 20 by 60
- The maximum area is 1200 square feet
From the figure (see attachment), the perimeter is:

The perimeter is given as: 120.
So, we have:

Make y the subject

The area is then calculated as:

Substitute 


Differentiate

Set to 0

Rewrite as:

Divide through by 6

Recall that: 
So, we have:



The dimension that maximizes the area is 20 by 60
The area is calculated as:

So, we have:


Hence, the maximum area is 1200 square feet
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