Answer: {C, O, L, E, T, I, N}
Step-by-step explanation:
We simply list each letter one time. Any duplicates are tossed. If you sorted the letters alphabetically, then you'd get {C, E, I, L, N, O, T}. However, the order doesn't matter with sets.
Note: This listing method is another name for "roster method". Think of how sports teams list their roster, which is basically just a list of the players' names.