Notice that -10 is a constant, meaning that it is not going to be influenced by , or the number of cheeseburgers sold at the food stall. Thus, we can instantly eliminate Choice B.
Also, remember that the entire expression represents total money earned. This has nothing to do to with the number of cheeseburgers sold at the event, which includes the maximum that can be sold. Thus, Choice A is eliminated.
Let's consider what happens if we sell 0 cheeseburgers. Well, the first term is 0, leaving us with a total money balance of -10. -10 surely doesn't represent money earned (how would you earn negative money?), which eliminates Choice D.
We can say that our answer is Choice C because it is the only choice left. However, we can also figure that when 0 cheeseburgers were sold, there was a negative amount of money earned. What would cause this? Well, the <em>cost </em>of setting up the food stall, since that will be represented as a negative profit, or money lost.