9. Two statistics students went to a flower shop and randomly selected 12 carnations. When they got home,
the students prepared 12 identical vases with exactly the same amount of water in each vase. They put one
tablespoon of sugar in 3 vases, two tablespoons of sugar in 3 vases, and three tablespoons of sugar in 3
vases. In the remaining 3 vases, they put no sugar. After the vases were prepared, the students randomly
assigned one carnation to each vase and observed how many hours each flower continued to look fresh. A
scatterplot of the data is shown above. The least-squares regression line for these data is
= 180.8 + 15.8x.