Which function has the higher rate of change over the interval [0,3]

Since the average rate of change of a function is the slope of the associated line we have already done the work in the last problem. That is, the average rate of change of from 3 to 0 is 1. That is, over the interval [0,3], for every 1 unit change in x, there is a 1 unit change in the value of the function.