how to write code solve this linear equations?

I am now doing some machine vision, and this application need some code to solve linear equations, I am poor at matlab coding and math. I have search many, but more confused, does any body know how to solve these problem likly? thank you!

[Walter Roberson]

Where did the 4th column of A come from? The diagram shows it as 3 x 3.

[dcscodelife]

Sorry, I showed it incorrectly. The second screenshot of matlab is test for solving linear equations, it is not related to original questions, just for matlab coding. I mean that here X1 should be X1=gX where g should be a scale number. but matlab get [-2 8 -4 0]' , I cant understand it because it not as X1=gX formation.