Can someone help & explain. I don’t understand!!

     {2, 3, 4, 5, 6}

Step-by-step explanation:

You are expected to determine the digits of the given number, then list them between curly brackets. Even if a digit appears in the number more than once, you need list it only once. It is helpful to sort the elements of a set, but not necessary.

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The digits are 5, 3, 2, 6, 4, 6.

In sequence, the unique digits are 2, 3, 4, 5, 6.

The set of digits in the number is ...

  {2, 3, 4, 5, 6}

"Roster notation" means you simply list the elements of the set.