linear algebra - How to find the bases for two spanning sets and for their sum?

Let $u_1=(1,2,0,-1)$, $u_2=(0,2,-1,1)$, $u_3=(3,4,1,-4)$ and $v_1=(-2,-2,1,3)$, $v_2=(2,3,2,-6)$, $v_3=(-1,4,6,-2)$.

Let $H =span\{u_1,u_2,u_3\}$ and $K = span\{v_1,v_2,v_3\}$.

In here I have to find bases for $H$, $K$ and $H+K$.
I can't understand how to do it.
I wrote vectors in $H$ and $K$ as linear combinations.
Then I think I have to prove that those vectors are linearly independent.
But I don't know how to do it.
Can you help me to find an answer for this question?