Suppose There Is a Competitive Market for Retail Workers at a Large

Suppose there is a competitive market for retail workers at a large shopping mall that is large enough to constitute its own labour market. The labour demand curve is QD = 1000 - 20(w) . The labour supply curve is QS = 400 + 40(w) . Suppose that a union now successfully organizes the workers at this mall and obtains a wage rate of $11 (but does not affect the demand curve) . The number of workers who wish to work at the new wage is _.

A) 780
B) 400
C) 440
D) 1000
E) 840