An exchange rate is used to​

 how much of your country's currency buys another foreign currency. For some countries, exchange rates constantly change, while others use a fixed exchange rate. The economic and social outlook of a country will influence its currency exchange rate compared to other countries.

Explanation:

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exchange rate. the price of one country's currency in terms of another country's currency; facilitates trade; doesn't affect money supply but affects the price of money.

Explanation:

tried to make it simple as possible :)

answer would be b, a tariffs main purpose is to protect domestic production and jobs.