Algebraic Manipulation !

Geometry Level 5

Let $x\in \mathbb{R}^{ + }$ and $f\left( x \right) = \sqrt { 576+{ x }^{ 2 }-24x } +\sqrt { 49+{ x }^{ 2 }-7\sqrt { 3 } x }$ .

If we set $x$ positive variable in such a way that $f\left( x \right)$ is Minimum possible, then for this condition, find the value of $E\quad =\quad \frac { 336-24\sqrt { 3 } x -7x }{ 4 } .$