The assessment rates (in percentages) assigned to a random sample of 40 commercially zoned parcels of land

Question:

The assessment rates (in percentages) assigned to a random sample of 40 commercially zoned parcels of land in the year 2012 are stored in the data file Rates.
a. What is the standard deviation in the assessment rates?
b. Approximately what proportion of the rates will be within ± 2 standard deviations of the mean?