Five hundred dollars, please. And could you give me ten dollar in small change?
请换500美元。再另外能否给我10元的小面额零钱?
It is better to ask for help at the beginning rather than to wait until a busy period when everyone is rushed off their feet.
最好在开始工作时就请人帮忙,而不是等到大学都忙得不可开交的时候。