Really simple problem - rearranging equations, getting it upside down.

Hey I know this is really simple and silly, I used to find this really easy, I've been confused by a book and now feel rather stupid at not being able to even rearrange equations.. I get it right, right, right and then suddenly I get one written exactly upside down when compared to the book's answer.

Here's an upside down one:

to make the subject

I did

then

then

or

Their answer was

I've spent a few hours rereading my chapters and getting a bit upset...what have I done wrong? (Doh)