Application Of Derivatives

Let the maximum and minimum values of \(\left(\sqrt{8 x-x^2-12}-4\right)^2+(x-7)^2, x \in \mathbf{R}\) be \(\mathrm{M}\) and \(\mathrm{m}\), respectively. Then \(\mathrm{M}^2-\mathrm{m}^2\) is equal to _________.