The average rate of change of a function between two points and the slope between two points are the same thing. Compare the two lines you have drawn. The x represents the starting point of your interval.
You da real mvps.
The slope of the secant line passing through the pointsP15250 andQ10444is 388 and the slope of the secant line passing through the pointsP15250andQ20111is 278. The slope of the secant line is D y D x. So i know the slope of the line m is equal to the slope of the line n because they are parallel. Compare the two lines you have drawn.