Hello,

1. I've attached a sketch of the described swimming pool.

2. . Thus:

3. The area including the decks is:

. Now plug in the value of l:

4. . Expand the RHS of this equation:

5. This function has an extreme value (maximum or minimum, you are interested in the minimum) if the first derivative equals zero:

. Solve for w:

I've got: w = 30. Plug in this value to calculate l. I've got l = 60.

EB