(a) The marginal product of labor is the slope of the production function. As the quantity of labor increases, the marginal product decreases, from MP_L = 1 when L = 1 to MP_L = 0.45 when L = 5 and the slope flattens.(b) Using the production function in panel a, we can derive the marginal-product-of-labor curve. The downward slope of the curve shows the diminishing marginal returns to labor.