✓ Mathematica : cpu = 0.0067519 (sec), leaf count = 24
DSolve[4*Derivative[1][y][x]^2 - 2*(y[x] + 3*x*Derivative[1][y][x])*Derivative[2][y][x] + 3*x^2*Derivative[2][y][x]^2 == 0,y[x],x]
✓ Maple : cpu = 0.661 (sec), leaf count = 36
dsolve(3*x^2*diff(diff(y(x),x),x)^2-2*(3*x*diff(y(x),x)+y(x))*diff(diff(y(x),x),x)+4*diff(y(x),x)^2=0,y(x))