$${\mathtt{D}} = {\sqrt{{{\mathtt{a}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{{\mathtt{b}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{{\mathtt{c}}}^{{\mathtt{2}}}}}$$
http://www.schulminator.com/mathematik/wuerfel-und-quader
= $${\frac{{\mathtt{1}}}{{\mathtt{55}}}}{\mathtt{\,\times\,}}\left({\mathtt{\,-\,}}{\mathtt{28}}{\mathtt{\,\small\textbf+\,}}{\mathtt{8}}{\mathtt{\,-\,}}{\mathtt{24}}\right) = {\frac{{\mathtt{1}}}{{\mathtt{55}}}}{\mathtt{\,\times\,}}\left(-{\mathtt{44}}\right) = {\mathtt{\,-\,}}{\frac{{\mathtt{44}}}{{\mathtt{55}}}} = {\mathtt{\,-\,}}{\frac{{\mathtt{4}}}{{\mathtt{5}}}}$$