(y_final-y_start)/(x_final-x_start) always! :) that easy
(-6-2)/(2-0) = -4
You probably know that if the interval was pretty small, between 0 and 0.0001, it would take you to the concept of slope and derivatives, but average change is just ignoring anything in between x=0, and x=2 (it could go up/down million times, and still the answer would be -4)
