The height of a plant, y , in centimeters, is measured x weeks after planting a seed. The height can be modeled by the regression equation y is equal to the fraction with numerator 6 point 8 8 and denominator 1 plus 2 comma 139 point 9 9 e raised to the negative 0 point 4 7 x power Which statement best interprets the value 6 point 8 8 ?