Gloria has a gallon of paint to cover 500 square feet of drywall. She pointed out that for 10,000 square feet she needs 20 gallons of paint. Let's say the output (the range) is going to tell us how many gallons of paint to buy at the hardware store. The input will be the square footage required to be covered in the paint. Can someone write a function that describes this relationship?

Gallons = Area/500

The "output" is the dependent variable. The "input" is the square feet of area to be painted. Output has nothing to do with range.

You appear to be taking a poorly taught algebra class.