Let ${\rm{I}}(x) = \int {\frac{{dx}}{{{{(x - 11)}^{\frac{{11}}{{13}}}}{{(x + 15)}^{\frac{{15}}{{13}}}}}}} \cdot $. If ${\rm{I}}(37) - {\rm{I}}(24) = \frac{1}{4}\left( {\frac{1}{{\;{{\rm{b}}^{\frac{1}{{13}}}}}} - \frac{1}{{{{\rm{c}}^{\frac{1}{{13}}}}}}} \right),{\rm{b}},{\rm{c}} \in $, then $3(\;{\rm{b}} + {\rm{c}})$ is equal to