\[ \left \{x'(t)+y'(t)+y(t)=f(t),x''(t)+x(t)+y''(t)+y'(t)+y(t)=g(t)\right \} \] ✓ Mathematica : cpu = 0.0772944 (sec), leaf count = 44
\[\left \{\left \{x(t)\to -f''(t)-f'(t)-f(t)+g'(t)+g(t),y(t)\to f''(t)+f(t)-g'(t)\right \}\right \}\]
✓ Maple : cpu = 0.027 (sec), leaf count = 48
\[ \left \{ \left \{ x \left ( t \right ) =-{\frac {\rm d}{{\rm d}t}}f \left ( t \right ) +g \left ( t \right ) -f \left ( t \right ) -{\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}f \left ( t \right ) +{\frac {\rm d}{{\rm d}t}}g \left ( t \right ) ,y \left ( t \right ) =f \left ( t \right ) +{\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}f \left ( t \right ) -{\frac {\rm d}{{\rm d}t}}g \left ( t \right ) \right \} \right \} \]