Short Answer 
Both participants initially invest $20 each, totaling $40 for a shared resource. After selling the box for $30, each person ends up with $10 less than their original investment, resulting in a loss of $10 for both and no profit from the transaction.
Step 1: Initial Contributions
Both participants start by investing an equal amount of money. Initially, each person contributes $20 to create a shared resource, leading to a combined total of $40. This sets the foundation for the upcoming transaction and represents their initial stake in the box.
Step 2: Selling the Box
The box is sold for $30 to one person, who now effectively owns the box containing their original $20 contribution along with the other person’s contribution. The buyer has exchanged $30 for the box but has, in reality, taken on a financial burden since they spent more than their initial investment.
Step 3: Post-Transaction Positions
After selling the box, neither participant benefits financially. Here’s the breakdown of their financial status:
- Person A ends up with their original $20 in the form of cash but incurred a loss of $10 since they had put $20 in the box.
- Person B retains their original $20, but after paying $30 for the box, they also experience a loss of $10.
In conclusion, both participants are effectively $10 down with no profit made in the transaction.