The vector \(\vec{b}\) is not in the span of the other vectors.

RREF of vectors augmented by \(\vec{b}\):

\vec b = 
\begin{bmatrix} 
 2  \\ 
 1  \\ 
 -1
\end{bmatrix}

Vectors:

\begin{bmatrix} 
 -2  \\ 
 1  \\ 
 -4
\end{bmatrix} \quad 
\begin{bmatrix} 
 10  \\ 
 -5  \\ 
 20
\end{bmatrix} \quad 
\begin{bmatrix} 
 4  \\ 
 2  \\ 
 1
\end{bmatrix} \quad 
        

\begin{solution}
The vector \vec{b}  is not  in the span of the other vectors.
\[
\begin{bmatrix} 
1 & -5 & 0 & 0   \\ 
0 & 0 & 1 & 0   \\ 
0 & 0 & 0 & 1
\end{bmatrix}
\]
\end{solution}