\[
\boxed{
4\, \left( y \left( x \right)  \right) ^{2}{\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left( x \right) -18\,y \left( x \right)  \left( {\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) +15\, \left( {\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) ^{3}=0}
\]