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Math·Problem-Solving and Data Analysis·Two-variable data: Models and scatterplots

hard

The scatterplot shows data set A, which consists of the weights $y$, in pounds, of a Labrador retriever puppy at various ages, $x$, in months. The equation of a line of best fit for the relationship in data set A can be written as $y=-5.0+8.7x$, where $2\le x\le 6$. The puppy was weighed again at 9 months old and weighed 52 pounds. Data set B consists of all the data points in data set A as well as the data point $(9,52)$. The equation of a line of best fit for data set B can be written as $y=r+sx$, where $r$ and $s$ are constants and $2\le x\le 9$. Assuming the equations of the lines of best fit are calculated in the same way, which of the following is the best estimate for the value of $s$?

A

5.8

B

8.7

C

13.7

D

17.7