Assume that the price of silk ties in a perfectly competitive market is $21 and that the typical firm confronts the following costs:

Quantity

(ties per day) 0 1 2 3 4 5 6 7 8 9 10 Total cost $10 $17 $26 $37 $50 $65 $82 $101 $122 $145 $170

(a) What is the profit-maximizing rate of output for the firm?

(b) How much profit does the firm earn at that rate of output?

(c) If the price of ties fell to $15, how many ties should the firm produce?

(d) At what price should the firm shut down?