I have a question for my algebra class that states: At O'Donnells Restaurant you can order Chicken Nuggets in packs of 6, 9, or 20 (i.e. if you buy two 9 packs you have 18 nuggets, if you buy one 6 pack and three 20 packs you would have 66 nuggets, etc.) The teacher also told the class that the answer is under 1000 nuggets
And the question that is being asked is, What is the greatest number of nuggets you cannot order?
I don't need the answer, I just need a way to go about solving the problem.