Given f(x)=x2+4x\displaystyle {f{{\left({x}\right)}}}={x}^{{2}}+{4}{x}, find the average rate of change of f(x)\displaystyle {f{{\left({x}\right)}}} on the interval [4,4+h]\displaystyle {\left[-{4},-{4}+{h}\right]}. Your answer will be an expression involving h\displaystyle {h}.