A carpenter makes wooden chairs.
He has enough wood to make 30 chairs.
He makes $60 profit on a dining chair and $90 profit on a rocking chair.
It takes him 1 hour to make a dining chair and 2 hours to make a rocking chair.
He only has 40 hours available to work on the chairs.
The carpenter wants to maximize his profit given the constraints. He draws the graph below to represent this situation.