What is the dimension of the subspace of R4\mathbb{R}^4R4 spanned by {(1,1,0,0),(0,0,1,1),(1,1,1,1)}\{(1, 1, 0, 0), (0, 0, 1, 1), (1, 1, 1, 1)\}{(1,1,0,0),(0,0,1,1),(1,1,1,1)}?
111
222
333
444