When might it be important to know a currency’s exchange rate?
a) when planning expenses for an overseas trip
b) when changing money into smaller denominations
c) when preparing to buy something expensive
d) when deciding which college is the best value

The correct answer of the given question above would be the first option. It is important to know a currency's exchange rate when you are planning for the expenses for an overseas trip. When you are overseas, the money you will be using should be exchanged for the currency depending on where you travel and currency changes from time to time and differs from country to country so it is necessary to know the rate beforehand. Hope this answer helps.

Complementary goods. they go together, thats why one price increase and the others demand increases