A marketing firm conducts a survey to determine the ages of their survey subjects who like a new health drink.

This is the resulting data from their survey:

49, 63, 78, 22, 41, 39, 75, 61, 63, 65,

58, 37, 45, 52, 81, 75, 78, 72, 68, 59,

72, 85, 63, 61, 75, 39, 41, 48, 59, 55,

61, 25, 61, 52, 58, 71, 75, 82, 49, 51

The standard deviation of the dataset is [a]