Can you please help me describe an an everyday situation between variables that is a function and help me explain why the relationship is a function?

Here is what the teacher provided.

When you buy your favorite type of chocolate you are charged by how much you want. The cost is therefore a function, because it depends on the number of ounces of chocolate you buy. That is, for each input (weight in ounces), there is one output (cost, say in dollars). By contrast the price of a house is not a function of the lot size on which a house is built because houses on the same size lot may sell for many different prices.

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