How to decide if the system Ax b has solutionsa unique solu

How to decide if the system Ax = b has solutions/a unique solution/no solution? - Understand what is Gaussian elimination method (only focus on the without-pivot version), and how to implement it in MATLAB;

https://www.dropbox.com/s/i3t80is3kq3wlqj/120.bmp?dl=0

https://www.dropbox.com/s/n9aexzk8t2pm7ux/121.bmp?dl=0