Answer:

Step-by-step explanation:
Expression for the rectangular area and perimeter are, respectively:


After some algebraic manipulation, area expression can be reduce to an one-variable form:


The first derivative of the previous equation is:

Let the expression be equalized to zero:


The second derivative is:

According to the Second Derivative Test, the critical value found in previous steps is a maximum. Then:

The maximum area is:


To find the weight of 1 load of stone, divide 2/3 by 4.
To divide fractions, use keep change flip.
Keep the first fraction the same, change the division sign into a multiplication sign, and flip the second fraction.
I attached the work and answer for this problem. If you have any questions please feel free to ask.
Hope this helps.
Answer: 11 2/15
Explanation: (3+7) (1/3+4/5)
10 + 17/15
10 + 1 2/15
11 2/15