Optimal extraction rate. Suppose that the capital-output ratio is constant and that the real interest rate takes the constant value r. Using the energy model in Section 10.1, solve for the constant rate of extraction s*E that maximizes the present discounted value of output per worker. Explain and interpret your result. (Hint: notice that output per worker grows at a constant rate, so that this present value is relatively easy to compute. Assume r is suffi ciently large.)