(a+3a+ 5a+```+2007a)-(2a+4a+6a+```+2008a)=?

(a+3a+ 5a+```+2007a)-(2a+4a+6a+```+2008a)=?
(a+3a+ 5a+```+2007a)-(2a+4a+6a+```+2008a)
等于多少?写出过程和代数式,