At What Level of Effort Does Performance Based Pay in the Form

At what level of effort does performance based pay in the form of salary-plus-commission yield the maximum payoff to an employee?

A) 40 hours per week
B) As much as the employee can possible work
C) When the slope of a line tangent to the cost curve is one half of the slope of the salary curve
D) There is no effort level at which an employee can maximize their payoff given a salary-plus-commission pay construct
E) When personal marginal benefit equals personal marginal cost