Linear Programming

So you work at a toy factory making toy cars and trucks. You get a bonus of 30 cents for each car that you make and 80 cents for each truck that you make in a day. You have to make at least 6 cars every day, but can make no more than 6 cars, and no more than 5 trucks. To add to all of the confusion, each vehicle needs labels, of which you only have 21 per day to use. Each car needs 2 labels and each truck needs 3 labels.
Where did this occur? If we change the bonuses, can we change where this occurs? Is there a pattern to where the maximum bonuses are achieved? Why is this?