Nancy is willing to bake one batch
of cookies per day if she can sell it for at least $7.
She can make these cookies at a time when she has
little else to do. To make a second batch per day, she
has to give up dusting her house, which is mildly
important to her, so she will not bake the second
batch unless she gets at least $10. To bake a third
batch, she would have to give up some phone calls to
friends, so she will not bake a third batch unless she
can sell it for at least $12. Finally, to bake a
fourth batch, she would have to stop watching a soap
opera, so she would not bake it unless she can sell it
for at least $20. Suppose that she finds she can sell
cookies at $15 per batch.