A manufacturer has received an order to make 400000 souvenir key chains commemorating the anniversary of the first landing of the moon. The firm owns several machines, each of which can produce 200 key chains per hour. The cost of setting up the machines to produce the medals is $80 per machine, and the total operating cost is $5.76 per hour.

A) Express the cost of producing 400000 medals as a function of the number of machines used.

B) Draw the graph and estimate the number of machines the firm should use to minimize cost