Statistics - line of regression?

The simplest measure of spread is equal to the difference between the largest and the smallest values. Your x values are spread over the range [13,23]. Within this range your estimated y values spread in the range of [4.05-0.06*23, 4.05-0.06*13] = [2.67,3.27] So the difference between the largest and smallest values of the estimated values y could take is 3.27-2.67=-4.05-0.06*13 - (4.05-0.06*23) = 10 * 0.06 = 0.6