.0 billion . assets declined 36% ( 36 % ) versus the prior year , primarily driven by amortization and prepayments , sales , marks and charge-offs . asset sales during the fourth quarter of 2009 ( $ 10 billion ) were executed at or above citi 2019s marks generating $ 800 million in pretax gains for the quarter . 2008 vs . 2007 revenues , net of interest expense decreased $ 21.7 billion , primarily due to negative net revenue marks . revenue included $ 14