Initially, When a Firm Hires a Fourth Worker, Its Wage

Initially, when a firm hires a fourth worker, its wage rate goes from $80 a worker to $90. The marginal revenue product of the fourth worker is $100. Then the government imposes a minimum wage of $90 a worker. If the firm now hires the fourth worker, its profits will

A) will increase by $10.
B) will increase by $20.
C) will decrease by $10.
D) will decrease by $20.