Suppose the production of a firm is modeled by $P(k, l)=16 k^{1 / 3} l^{2 / 3},$ with $k$ and $l$ defined as in example 5.2. Suppose that $l=3$ and $k=4,$ the labor force is increasing at the rate of 80 workers per year and capital is decreasing at the rate of $ 200,000$ per year. Determine the rate of change of production.