38 Marginal effect of additional year of experience becomes negative after years of experience. a 31.4 b 29.9 28.5 27.1 39 A black worker earns % less than a white worker. a -13.91% b -13.00% C - 12.15% -11.35% 40 A female worker earns % less than a male worker. a -18.01% b -16.99% C -16.03% -15.12%