Which one of the following is NOT a proper subset of {3, 4, 5}?

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6 + 7 =
Solve this simple math problem and enter the result. E.g. for 1+3, enter 4.

Which one of the following is NOT a proper subset of {3, 4, 5}?

{3, 4, 5}

{4}

{3}

{3, 4}