Jacob and Zain take pencils from a box of $$21$$ pencils without replacing them. On Monday Jacob takes $$\frac{2}{3}$$ of the number of pencils that Zain takes. On Tuesday Jacob takes $$\frac{1}{2}$$ of the number of pencils that Zain takes. On Wednesday morning the box is empty. How many pencils does Jacob take? 
选项为:A:$$8$$  B:$$7$$  C:$$6$$  D:$$5$$  E:$$4$$  请回答其中一个选项.