A copy machine dealer has data on the number x of copy machines at each of 89 customer locations and the number y of service calls in a month at each location. Summary calculations given are X bar=8.4, Sx=2.1, Y bar=14.2, Sy=3.8, and r=0.86. What is the slope of the least-squares regression line of number of service calls on number of copiers?
a. 0.86
b. 1.56
c. 0.48
d. None of these
e. Can't tell from the information given
Answer: b. 1.56