given the function, there is no independent variable, x. Because of that your equation remains constant at the y axis, where you get f(x)=57. This means that for any input of x you’ll get 57 as the output. Because youre looking for average rate of change, you would use delta y/ delta x.
(2,57) and (6,57)
When you solve for change between the y and x, you get (57-57)/(6-2
) which ultimately gives you an average rate of change of 0.