某工程甲单独完成要45天，乙单独完成要30天，若乙先单独干22天，剩下的由甲单独完成．问甲、乙一共用几天可以完成全部工作，若设甲、乙共用x天完成，则符合题意的方程是（　　）

— Sam has heard of this story before.

— _________.

-- How did your class raise money for the poor old man in hospital?

-- We organized a book fair on the playground and sold some books and CDs.