Robin is deciding between two data plans. Phones Unlimited offers a plan for $20 per month for the first 500 megabytes of data and $2 per month for each additional 500 megabytes. Cells United offers a plan that costs $10 per gigabyte (1000 megabytes).
1. Write a function to model each of the data plans. Define the variable(s) in each function.
2. How much data would Robin have to use to make the Phones Unlimited data plan cheaper than the Cells United data plan?