4. Some people think that the behavior of the stock market in January predicts its behavior for the rest of the year. Take the explanatory variable x to be the percent change in a stock market index in January and the response variable y to be the change in the index for the entire year. We expect a positive correlation between x and y because the change during January contributes to the full year's change. Calculation from data for an 18-year period gives x = 1.75 % y = 9.07% S, = 5.36% Sy = 15.35% r = 0.596 a. Find the equation of the least-squares regression line. b. Use your regression line to predict the change in the index in a year in which the index rises 1.75% in January. Why could you have given this result without doing the calculation