Economics problem

Cost Accountant (Student) (92 Points)

06 December 2013  

Hello, here's an economics querry...

 For profit maximization, firms should continue producing more output until marginal revenue equals marginal cost. That’s the point where profits are maximized.

My question is, when MR=MC, marginal profit ie MR-MC=0. When marginal profit is zero, how can it be profit maximization ? ?