Let the supply and demand for widgets be given by the following schedule.

Price: 3, 4, 5, 6, 7, 8, 9, 10, 11

Quantity Supplied: 100, 200, 300, 400, 500, 600, 700, 800, 900

Quantity Demanded:900, 800, 700, 600, 500, 400, 300, 200, 100

1. What quantity will be produced here?

2. What quantity is efficient if there are no external costs or benefits?

3. What quantity is efficient if there is an external cost of $2 per unit from pollution caused by the widget factories?