Easy# What Does This Augmented Matrix Tell You?

LINALG-N3OKVI

The matrix below is the reduced row echelon form of the augmented matrix representing a linear system. Which one of the following must be true about the system?

$$\left [\matrix { 1 & 0 & 2 & 3\cr 0 & 1 & 0 & 5 \cr 0 & 0 & 0 & 6} \right ]$$