Is this problem factored completely correctly?

3a^3+6a^2-2a-4

(3a^3)+(-2a-4)

(3a^3/3a^2+6a^2/3a^2)+ (-2a/-2-4/-2)

3a^2(a+2)+ -2(a+2)
(1a+2)(3a^2+-2)

How would you write the final answer?