Answer to the question - This is an example of money as a medium of exchange and a unit of account .

Explanation to the answer - Money serves various functions. Primary functions of money are - • Medium of exchange - Money acts as an intermediary between the buyer and the seller. • Unit of account - Money provides a common yardstick to measure different units in a common denomination and serves as the common base of comparison. • Store of value - Money has the ability to retain its value over time.

?????????? Here in the above case/ question, each child can use the credit of $20 to purchase snacks from the snack shop. So, the money (credit of $20) can be used as the medium of exchange (between children and the snack shop owner). Second thing, as the purchases are being recorded, so the each child can purchase snacks valued upto $20 (credit of $20) only. Here, money serves the function as a unit of account.

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