In each question, the first and the last sentences of the passage are numbered S1 and S6 respectively. The rest of the passage is split into four parts. These four sentences are jumbled. Read the sentences and identify their correct and logical order.

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S1: Payment for imports and exports is made through a system called foreign exchange.
P : The value of the money of one country in relation to the money of other countries is agreed upon.
Q : These rates of exchange vary from time to time.
R : For instance, an American dollar or a British pound sterling is worth certain amounts in the money of other countries.
S : Sometimes a United States dollar is worth 12 pesos in Mexico.
S6: Another time it may be worth eight pesos.
The Proper sequence should be: