✓ Mathematica : cpu = 0.0087725 (sec), leaf count = 74
DSolve[(-a - x)*y[x] + 8*Derivative[1][y][x] + 16*x*Derivative[2][y][x] == 0,y[x],x]
✓ Maple : cpu = 0.134 (sec), leaf count = 37
dsolve(16*x*diff(diff(y(x),x),x)+8*diff(y(x),x)-(x+a)*y(x)=0,y(x))