\[
\boxed{
4\,{\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left( x \right) -8\,{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) -11\,{\frac {\rm d}{{\rm d}x}}y \left( x \right) -3\,y \left( x \right) +18\,{{\rm e}^{x}}=0}
\]