At what points is the marginal benifit of applying additional fertilizer no longer grater than the marginal cost of the fertilizer

You work as the sales manager for a company that sells office supplies to businesses of all sizes. because the profit margins are razor-thin, you need to ensure that you are getting the very best prices on paper, pencils, pens, post-it notes, and other office supplies from the manufacturers. when reviewing the quarterly profit statement, you realize that your costs are higher than they should be, and you trace the higher costs back to an employee who has been lax about getting competitive bids to ensure the lowest prices. when you conduct your research to determine the reason for the higher costs, and take action to bring those costs back down, in which of the key management processes are you taking part?