Year  Snowfall in inches
2001    11
2002    15
2003    19
2004    17
2005    23
2006    20
2007    17
2008    13
2009    18
2010    21





A town's yearly snowfall in inches over a 10-year period is recorded in this table.

What is the mean of the snowfall amounts?

a. 16.4 in.
b. 17.1 in.
c. 17.4 in.
d. 18.1 in.