A marketing manager wishes to determine whether a relationship exists between the number of cereal boxes (Y) sold at the company's retail store and the number of clerks on duty (X) per day. The sample data below will be used to examine this empirical problem. Calculate the slope of the regression line.
X Y
3 4
2 4
2 2
1 2
a. 0
b. 1
c. 2
d. None of the above