im not sure where the expression is but given the number of Indian rupees you receive when you exchange at the local currency exchange.

say we have $1 cad and get 2 Indian rupees then we would have xy=s meaning that if we have x cad and the conversion rate is 2x or if its 1.2 Indian rupees then it is 1.2 for y and s is the amount you receive when you exchange.

same if the exchange rate is $1 cad for $1.20 USD then it is 1.2x=s so if you give 1 CAD you get $1.2 USD