2 Quick SQL Questions: Paginate Conditions and Adding to Value

I have 2 quick SQL questions that all my googling couldnt come up with
an answer

1. Paginate results based on 2 conditions

I currently have sorthelper sorting based on title/author. I'd like
the option to select based on 3 genres then be able to sort that
through those results by title. I haven't be able to see how to handle
sorting with a variable condition. (codes below

2. How to add to current value

How would I add to a current value in my table?

value = value.current + value.new