\[
\boxed{
 \left\{ {\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}x \left( t \right) +x \left( t \right) +y \left( t \right) =-5,{\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}y \left( t \right) -4\,x \left( t \right) -3\,y \left( t \right) =-3 \right\} }
\]