How to get the simplest form of this radical expression: $3\sqrt[3]{2a} - 6\sqrt[3]{2a}$. How to get the simplest form of this radical expression: 
$$3\sqrt[3]{2a} - 6\sqrt[3]{2a}$$
Here is my work:
$$3\sqrt[3]{2a} - 6\sqrt[3]{2a}$$
Since the radicands are the same, we just add the coefficients. 
$$-3\sqrt[3]{2a} \sqrt[3]{2a}$$
Since everything is under the same index it becomes:
$$-3\sqrt[3]{2} \sqrt[3]{a}$$
Did I do this correctly, if not can anyone tell me what I should do?
Thanks :-).

$$3\sqrt[3]{2a}-6\sqrt[3]{2a}=\sqrt[3]{2a}(3-6)=\sqrt[3]{2a}(-3)= -3\sqrt[3]{2a}$$
