SAT One-variable data Question

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 $y=-5.1+8.7x$ , 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 $s$ ?