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