(a) Find a basis for the subspace $\mathbf{S}$ in $\mathbf{R}^{4}$ spanned by all solutions of
$$
x_{1}+x_{2}+x_{3}-x_{4}=0
$$
(b) Find a basis for the orthogonal complement $\mathbf{S}^{\perp}$.
(c) Find $b_{1}$ in $\mathbf{S}$ and $b_{2}$ in $\mathbf{S}^{\perp}$ so that $b_{1}+b_{2}=b=(1,1,1,1)$.