\[ 4 y^{(3)}(x)-8 y''(x)-11 y'(x)-3 y(x)+18 e^x=0 \] ✓ Mathematica : cpu = 0.0708775 (sec), leaf count = 38
\[\left \{\left \{y(x)\to e^x+c_1 e^{-x/2}+c_2 e^{-x/2} x+c_3 e^{3 x}\right \}\right \}\] ✓ Maple : cpu = 0.025 (sec), leaf count = 23
\[\left \{y \left (x \right ) = c_{1} {\mathrm e}^{3 x}+{\mathrm e}^{x}+\left (c_{3} x +c_{2}\right ) {\mathrm e}^{-\frac {x}{2}}\right \}\]