Economics short answer type 3 questions

(a) Who demands the U.S. dollar in a freely floating rate system?
(b) For few months prior to your vacation trip to Mexico, you find that the exchange rate for your U.S. dollar has decreased relative to the peso. If you were a U.S. citizen or resident, are you saddened? Explain.
(c) Explain why a currency depreciation can improve a nation's balance of trade.