From Example RSB, form an arbitrary (and nontrivial) linear combination of the four vectors in the original spanning set for W

An arbitrary linear combination is

(You probably used a different collection of scalars.) We want to write y as a linear combination of

We could set this up as vector equation with variables as scalars in a linear combination of the vectors in B, but since the first two slots of B have such a nice pattern of zeros and ones, we can determine the necessary scalars easily and then double-check our answer with a computation in the third slot

Notice how the uniqueness of these scalars arises. They are forced to be 25 and −10.