From the file “Baltimore_Arts” get the number of art-related businesses per 1000 residents for Baltimore in 2011 and 2012 (artbus11 and artbus12 respectively).
a) Perform a paired t-test at 5% significance to determine if there is any difference between the 2011 and 2012 rates.
b) Construct a histogram of the differences. Does it seem that they follow a normal distribution?