\[ 4 y^{(3)}(x)-8 y''(x)-11 y'(x)-3 y(x)+18 e^x=0 \] ✓ Mathematica : cpu = 0.0244776 (sec), leaf count = 38
DSolve[18*E^x - 3*y[x] - 11*Derivative[1][y][x] - 8*Derivative[2][y][x] + 4*Derivative[3][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to e^x+c_1 e^{-x/2}+c_2 e^{-x/2} x+c_3 e^{3 x}\right \}\right \}\] ✓ Maple : cpu = 0.024 (sec), leaf count = 23
dsolve(4*diff(diff(diff(y(x),x),x),x)-8*diff(diff(y(x),x),x)-11*diff(y(x),x)-3*y(x)+18*exp(x)=0,y(x))
\[y \left (x \right ) = \left (x c_{3}+c_{2}\right ) {\mathrm e}^{-\frac {x}{2}}+c_{1} {\mathrm e}^{3 x}+{\mathrm e}^{x}\]