Attempting to analyze the relationship between costs and sales, the owner of a fashion shop recorded the monthly costs ($ thousands) and the sales ($ millions) for a sample of 15 months. And completed a regression model for Sales vs Costs (i.e. y=Sales, x=Costs) The coefficient of determination for this data is r² = 0.2559 and the regression equation is: y = -10.0629 - 0.5456x.

(a) What percent of the variation in sales cannot be explained due to the cost factors? (b) Calculate the correlation coefficient
(c) What is the slope of the equation?
(d) What would be the best predicted sales for the costs of $50,000? (Note X is is thousands) ($ millions)