If the function:

is typed correctly, then the derivative is equal to the derivative of:

We need to use the product rule here:

Factor the derivative:

Solving for the critical number you get:

x=2001.

so clearly something went wrong in my rushed reply here, because this does not agree with your book's answer. or... the original equation could be different and I misinterpreted the parentheses. I hope the procedure helps though.

Because you have a closed interval for the domain. You should compare the population values at the end points to the ones at the critical numbers.

Good luck!