87. A researcher wanted to determine if a daily dose of vitamin C (in mg) would affect a subject's red blood cell count (in million cells per mcL). Below is data for 5 subjects that participated in the experiment. --\"n Change in 0.46 0.42 0.50 0.45 0.44 Red blood cell count a. What is the explanatory variable in this experiment? b. Construct a scatterplot for the given data. c. Estimate the correlation (positive, negative, or no correlation) between the variables. 88. Describe the correlation (positive, negative, or no correlation) between the following variables. a. x = Height of a person, y == Weight of a person. b. x = Age of a used car, y = Value of a used car. c. x = Speed ofa car, y = Duration of travel. 89. A toy company is analyzing the relationship between the amount of sales (in thousands of dollars) and the amount spent on advertising (in thousands of dollars) during a particular scal year. a. Which of the two variables is the explanatory variable? b. Estimate the correlation (positive, negative, or no correlation) between the variables. c. If the equation of the least-squares line is y = 49.25 + 0.51x, estimate the amount of sales during a scal year where 70 thousand dollars is spent on advertising. 13