7. Basis for a sum of subspaces

Problem. In $\mathbb{R}^3$, if $W_1$ is spanned by $(1,2,1)$, $(2,4,2)$, $(1,3,3)$ and $W_2$ is spanned by $(2,7,8)$, and $(3,8,8)$, find a basis for $W_1 + W_2$.

Method. Just put these lists together and find a basis, as in Section or Section .