Number series: two operations alternate (x2 then +3, x2 then -2 ...)

This type of question, asked 4 times: 18 Sep 2024 S3, 18 Sep 2025 S1, 24 Sep 2025 S1, 26 Sep 2025 S3. All 4 questions below, oldest first.

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Question 1
18 Sep 2024 S3
16 $Select the number from among the given options that can replace the question mark (?) in the following series. 3, 6, 9, 18, 21, ?$
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Question 2
18 Sep 2025 S1
14 $Complete the series. 3, 5, 10, 12, 24, 26, ?$
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Question 3
24 Sep 2025 S1
25 $7, 14, 28, 35, 70, ?$
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Question 4
26 Sep 2025 S3
21 $Complete the series. 7, 14, 12, 24, 22, ?$
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Question 1