Finding average rate of change (in a graph ?)

if there is a question :
find the average rate of change function of x on the interval [a,b]

Ans) we can do this by understanding and Using these laws

    average = change in y-axis / change in x-axis 
                   = rise / run
                   = Δy / Δx
                   = f(b) - f(a) / b-a 

Thank You and have a nice day