Writing Common Functions from Graphs and Tables

Liz enjoys playing video games and occasionally buys them. A new game is set to come out in the near future, it's a bit pricey but since she's a big fan, she decides to start saving up.

The game will come out in approximately 12 weeks. The price now listed on the website, including shipping, is 280 dollars. Currently, Liz can put 20 dollars towards this cause. What is the least amount Liz has to save each week for the next 12 weeks, so she could afford the game when it comes out?