\[ \left \{x'(t)=a x(t),y'(t)=b\right \} \] ✓ Mathematica : cpu = 0.0180445 (sec), leaf count = 22
\[\left \{\left \{x(t)\to c_1 e^{a t},y(t)\to b t+c_2\right \}\right \}\] ✓ Maple : cpu = 0.055 (sec), leaf count = 19
\[\{\{x \left (t \right ) = c_{1} {\mathrm e}^{a t}, y \left (t \right ) = b t +c_{2}\}\}\]