Find a basis perpendicular to W.

Let $\displaystyle V = \begin{bmatrix}1\\-4\\1\\4\end{bmatrix} $ and $\displaystyle U = \begin{bmatrix}3\\-13\\3\\-4\end{bmatrix} $

and let W be the subspace spanned by V and U.

I am pretty confused on this topic right now :( I just dont seem to know what i need to do to solve problems like these.

Any help would be great :)

Thank you