Missing digit making a number divisible by 9

The same question, asked 2 times: 21 Jul 2023 S4*, 17 Sep 2024 S2. Every wording below, oldest first.

Try each one first, then open its answer.

Question 1
21 Jul 2023 S4
54 $Find the value of a to make 6234a6 divisible by 9.$
Tap an option to check your answer.
Question 2
17 Sep 2024 S2
51 $Find the least value of x for which 57x716 is divisible by 9.$
Tap an option to check your answer.