\[ \left \{x'(t)+y'(t)-y(t)=e^t,2 x'(t)+y'(t)+2 y(t)=\cos (t)\right \} \] ✓ Mathematica : cpu = 0.193649 (sec), leaf count = 71
\[\left \{\left \{x(t)\to -\frac {3}{4} c_2 e^{4 t}+c_1+\frac {3 c_2}{4}+e^t+\frac {5 \sin (t)}{17}-\frac {3 \cos (t)}{17},y(t)\to c_2 e^{4 t}-\frac {2 e^t}{3}-\frac {\sin (t)}{17}+\frac {4 \cos (t)}{17}\right \}\right \}\]
✓ Maple : cpu = 0.133 (sec), leaf count = 47
\[ \left \{ \left \{ x \left ( t \right ) ={\frac {{{\rm e}^{4\,t}}{\it \_C1}}{4}}+{\frac {5\,\sin \left ( t \right ) }{17}}-{\frac {3\,\cos \left ( t \right ) }{17}}+{{\rm e}^{t}}+{\it \_C2},y \left ( t \right ) =-{\frac {{{\rm e}^{4\,t}}{\it \_C1}}{3}}+{\frac {4\,\cos \left ( t \right ) }{17}}-{\frac {\sin \left ( t \right ) }{17}}-{\frac {2\,{{\rm e}^{t}}}{3}} \right \} \right \} \]