Suppose the production function of steel bookshelves is given by: f(L, K) = LK - 0.212 - 0.8K2 Suppose K = 20. (a) Graph the total product curve and the marginal product of labor curve. (b) Graph the average product of labor curve. At what level of labor input does this average productivity reach a maximum? How many bookshelves are produced at that point? (c) Does the bookshelf production function exhibit constant, increasing, or decreasing returns to scale