Given the augmented matrix in row echelon form:

$[A|b] = \begin{pmatrix} 1 & 2 & 3 & | & 5 \\ 0 & 1 & 4 & | & 2 \\ 0 & 0 & 0 & | & 0 \end{pmatrix}$

Which of the following statements about this system of linear equations is true?