In your own words, what's a function?

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Is this a function?
Explain your answer to #4.

Is this a function?
Explain your answer to #6.

Is this a function?
Explain your answer to #8.

Is this a function?
Explain your answer to #8.
Noah was at home. He got on his bike and rode to his friend’s house and stayed there for awhile. Then he rode home again. Then he rode to the park & back without stopping.
Sketch a graph of the story.
What's the independent variable?
When you input 8 hours, what is the output?
What's the dependent variable?