Consider the following table that describes the total cost of producing dresses by Shirley, a local fashion artist.
Dresses Total cost ($)
0 50
1 80
2 105
3 140
4 180
5 225
6 275
7 350
8 440
Assume that the market is competitive and the price of dresses is $64. At this price how many dresses should Shirley produce to maximise profit? (If Shirley is indifferent between producing an additional dress and not producing, please assume that she will produce the additional dress to break the tie.)