Missing digit for divisibility by 6 (even and digit sum)

This type of question, asked 3 times: 9 Sep 2024 S1, 13 Sep 2024 S1, 17 Sep 2024 S1. All 3 questions below, oldest first.

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Question 1
9 Sep 2024 S1
61 $217924k$
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Question 2
13 Sep 2024 S1
67 $If 321y72 is a multiple of 6, where y is a digit, what is the least value of y?$
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Question 3
17 Sep 2024 S1
70 $Find the least value of k for which a 7-digit number 249k876 is divisible by 6.$
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