X treat count (150, 200, 225, 250, 275, 300, 350, 400) Y prices (18, 21, 25, 28, 30, 31, 35, 45) .... coefficient r?, regression line where x= thread count n y= price in dollars... last, if the regression line is a useful predictor, estimate price of a sheet whose threcount is 500. is the predictor useful