If there is 3 percent frictional unemployment, 4 percent structural unemployment, and -2 percent cyclical unemployment, then the natural rate of unemployment equals:

Efficiency wages

a. raise the productivity of a firm's workers, so the firm hires more workers. b. raise the productivity of a firm's workers, so the firm hires fewer workers. c. reduce the productivity of a firms' workers, so the firm hires more workers. d. reduce the productivity of a firm's workers, so the firm hires fewer workers.

Suppose that Tom bought a bike from Helen for $195. If Helen's reservation price was $185, and Tom's reservation price was $215, the seller's surplus from this transaction was:

A. $10 B. $215 C. $195 D. $20