21. The article Effects of Bike Lanes on Driver and Bicyclist Behavior (ASCE Transportation Engrg. J., 1977: 243—256) reports the results of a regression analysis with x  available travel space in feet (a convenient measure of roadway width, de ned as the distance between a cyclist and the roadway center line) and separation distance y between a bike and a passing car (determined by photography). The data, for ten streets with bike lanes, follows:

x 12.8 12.9 12.9 13.6 14.5 y 5.5 6.2 6.3 7.0 7.8 x 14.6 15.1 17.5 19.5 20.8 y 8.3 7.1 10.0 10.8 11.0

a. Verify that xi  154.20, yi  80,

, xiyi  1282.74, and

b. Derive the equation of the estimated regression line.

c. What separation distance would you predict for another street that has 15.0 as its available travel space value?

d. What would be the estimate of expected separation distance for all streets having available travel space value 15.0?