Wage determination and interest income

-What should happen to the number of workers hired if a competitive employer's wages exceed its marginal revenue product (MRP)?

-When a Union requires certification to obtain a job, wages that workers receive are raised. Explain why?

-Suppose that firm A is a monopsony that demands labor and XYZ Union is a monopoly that provides labor. Other things constant, the equilibrium wage and quantity of labor will depend on what factor?

-Other things constant, at higher interest rates, the demand for capital decreases. Provide one reason why this happens.