I've been working through an Algebra book trying to re-teach myself...not doing a half-bad job. I've come to a problem I'm not sure I understand. I reach the right answer...but yet it's wrong. I've attached the problem, along with the way I've been working it into a MS Word doc file. Any insight as to where I'm going wrong, ruels I'm forgetting or clarification on how the book comes to the answer it does would be greatly appreciated!
A big thanks in advance!