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