\[ 4 y^{(3)}(x)-8 y''(x)-11 y'(x)-3 y(x)+18 e^x=0 \] ✓ Mathematica : cpu = 0.0324603 (sec), leaf count = 38
\[\left \{\left \{y(x)\to c_1 e^{-x/2}+c_2 e^{-x/2} x+c_3 e^{3 x}+e^x\right \}\right \}\]
✓ Maple : cpu = 0.021 (sec), leaf count = 26
\[ \left \{ y \left ( x \right ) ={{\rm e}^{x}}+{\it \_C1}\,{{\rm e}^{3\,x}}+{\it \_C2}\,{{\rm e}^{-{\frac {x}{2}}}}+{\it \_C3}\,{{\rm e}^{-{\frac {x}{2}}}}x \right \} \]