Please help me with the below question! Could you let me know how to determine the standard deviation here? Thanks

Example 1 (optimal order quantity): Suppose an item has this demand history below:

Demand History

36

41

32

60

49

52

36

31

47

66

24

68

42

Each selling season the item is ordered. Orders are placed only once a season. No reordering happens during the season. Suppose the selling price of $25 and the item has no markdown value. If the cost of the item was $20, what order quantity should the store consider for the next time the item is ordered?

My answers:

cost 20 retail 25 salvage 0 mu sigma Cu (retail-cost) (gain if have enough stock) 5 Co (cost-salvage) (loss if overstocked) 20 critical ratio (service level)(Cu/(Cu + 00)) 0.2000 2 service factor -0.8416 Q(optimal) 44.92307692