If you were to find percent change manually you would take an old original value and a new value find the difference between them and divide it by the original value. Add up 100 400 600 1100. While you have provided the correct end-result your explanation is incorrect.
Add up 100 400 600 1100.
When a best-fit regression line is calculated its binomial equation ymxb defines how the variation in the X variable explains the variation in the Y variable. The percentage of the variation of r 73 is R-squared 53 which is 53. Therefore the variance of the sample is 1166. The square of r.