Suppose That a Regional Health Authority Is the Only Employer

Suppose that a regional health authority is the only employer of nurses,and further,suppose that nurses are not unionized.The 625 currently employed nurses are paid $27 per hour.To attract an additional nurse,the employer must increase the wage to $28 per hour.The marginal cost of this additional worker is

A) $653.
B) $28.
C) $17 500.
D) $17 528.
E) $27.