solving system of equations using augmented matrix

[Marvin08]

I have a problem that i just can't seem to solve its an augmented matrix problem, and if anyone can help me i'd greatly appreciate it.
The Problem Is
2a-b-3c=-20
4a+2b+c=6
2a+b-c=-6

 

[stapel]

I have a problem that i just can't seem to solve

Please reply showing all of your steps and your answer, so we can try to find where you're making any errors. Also, please provide the book's answer. (It may be that you're right and the book is wrong!)

Thank you!

Eliz.