Use Named Ranges to build a table of results for the possible answers to the problem.

Explore what would happen for the other answers to the problem.

For the whole population, the result needs to be in square miles, and here we find the answer to the question.

At the person level, the most convenient unit of measure is feet, so we start there

First we put the assumption for the model in cells at the top of the sheet, rather than inserting those assumption into the middle of formulas.

The problem to model is shown here

Here is a video describing the problem