Peter’s Pills is the only chemist in a small town. Peter’s is located near the train station and gets a significant portion of its business from travellers changing train lines. The demand for toothpaste by local customers and travellers is given by the table below.

Peter’s can buy toothpaste from a wholesale supplier for $2 per tube.

To maximise its profits, Peter's should offer a discount (the difference between the price charged to travellers and the price charged to locals) equal to $_