A can of soda costs $1.25 in the United States and 25 pesos in Mexico. What is

Question:

A can of soda costs $1.25 in the United States and 25 pesos in Mexico. What is the peso-dollar exchange rate (measured in pesos per dollar) if purchasing power parity holds? If a monetary expansion caused all prices in Mexico to double, so that soda rose to 50 pesos, what would happen to the peso-dollar exchange rate?

Exchange Rate
The value of one currency for the purpose of conversion to another. Exchange Rate means on any day, for purposes of determining the Dollar Equivalent of any currency other than Dollars, the rate at which such currency may be exchanged into Dollars...