Help with 2 dvdr's to 1 double layer dvd

Hi everyone

I have Memoirs of a Geisha(2 dvd"s) and I’d like to put them on 1 dvd+r dl, and I was wondering how to go about doing that. I’ve searched and only seem to come up with splitting a dvd-9, fitting a dvd-9 to a single dvdr. I need 2 dvdr’s to 1 dvd-9.

Thanks in advance.