Three call options on a stock currently selling for $40 have the same expiration date and strike prices of $30, $40, and $50. The market prices are $13, $7, and $3 respectively.

1. Explain how a butterfly spread can be created from these three options.
2. Construct a table showing the payoff and profit from this strategy for different values of S_T.
3. Sketch the profit as a function of S_T.
4. For what values of S_T does the butterfly spread result in a loss?