Mrs Lee bought $$600$$ $$\text{g}$$ of flour.  She used some of it to bake some cookies.  She had $$21$$ $$\text{g}$$ of flour left.  How much flour did she use to bake the cookies?  She used~\uline{~~~~~~~~~~}~$$\text{g}$$ of flour to bake the cookies. 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying Addition and Subtraction->Simple Addition and Subtraction