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 Instructions: Enter your response as a whole number. (a) What is the profit-maximizing rate of output for the firm? (Choose the highest level of output.) ties/day (b) How much profit does the firm earn at that rate of output? $ (c) If the price of ties falls to $13, how many ties should the firm produce? ties/day (d) At what price should the firm shut down?