Mission complete!
You bought lemons, picked a fair price, and sold eleven cups. When Mr. Patel offered the shiny cups for all your coins, you said no thanks and kept some back. That is earning: work, plus a little planning. The two coins you saved are tomorrow's lemons.
Parent note
Maya practiced earning and chose to hold money back for later, unprompted. Dinner question: "If you ran the stand again tomorrow, what one thing would you change?"