Week 3 Challenges:
- Create a push button to sell ship. In the World, add code to sell ship for salvage value. Update # ships in databox and increase Bank account, and update Net Worth.
Hint: Use "delete agent__" block with " nearest agent__within 200 steps" block.
- Add a graph for "Bank Account" and "Net Worth" over time.
Extension: Add push buttons to show and hide graph.