To calculate how much you have spent in US dollars, you need to convert the Canadian dollars to US dollars.
First, calculate the cost of one glass of orange juice in US dollars:
Cost in US dollars per glass = (Cost in Canadian dollars per glass) * (Foreign per dollar) = 4.20 * 1.336 = 5.6112 US dollars
Then, calculate the total cost for 3 glasses of orange juice:
Total cost in US dollars = (Cost in US dollars per glass) * (Number of glasses) = 5.6112 * 3 = 16.8336 US dollars
Rounded to the nearest cent, you have spent approximately 16.83 US dollars.