Help plz! I dont understand this problem?

Abi has 20 cents. She bought x pencils for 3 cents each. If y is equal to the number of cents left, write an equation that shows the dependence of y on x. What is the domain of the function?

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Thanks!

Help plz I dont understand this problem Abi has 20 cents She bought x pencils for 3 cents each If y is equal to the number of cents left write an equation that class=