\[ y''(x)=-\frac {y(x)}{(a x+b)^4} \] ✓ Mathematica : cpu = 0.0543154 (sec), leaf count = 59
DSolve[Derivative[2][y][x] == -(y[x]/(b + a*x)^4),y[x],x]
\[\left \{\left \{y(x)\to c_1 e^{\frac {i}{a (a x+b)}} (a x+b)-\frac {1}{2} i c_2 e^{-\frac {i}{a (a x+b)}} (a x+b)\right \}\right \}\] ✓ Maple : cpu = 0.048 (sec), leaf count = 39
dsolve(diff(diff(y(x),x),x) = -1/(a*x+b)^4*y(x),y(x))
\[y \left (x \right ) = \left (a x +b \right ) \left (c_{2} \cos \left (\frac {1}{a \left (a x +b \right )}\right )+c_{1} \sin \left (\frac {1}{a \left (a x +b \right )}\right )\right )\]