When will he use up his chocolate milk account?

Brian's son buys chocolate milk every few days to go with his lunch. His school creates an invoice that they send to parents every month that show the status of his milk account. Brian put $20.00 into this account to start his son's sort-of-debit card ability. Begin writing linear equations with this data and process. When will his son's account go dry?

For Adventurer members we have an editable Word docx, an Excel sheet (with our data and graph), and solutions.