In Chicago 120 people are wants to work as cashiers if the wage is $6 a hour. For each $1 that the wage rises above $6 an additional 40 people are wants to work as cashiers.

For wages of $6, $7, $8, $9 and $10 per hour plot the labor supply curve for cashiers on a graph.

The reason why this labor supply curve is upward sloping is that:

1. Wages have to increase to accommodate union pressure
2. Higher wages attract workers from other industries
3. Labor production functions exhibit diminishing marginal returns
4. firms are willing to hire more workers at a lower wage