Shift grows letter by letter (+1, +2, +3 ...): code a new word

The same question, asked 4 times: 20 Jul 2023 S4*, 21 Jul 2023 S1*, 23 Sep 2024 S2*, 26 Sep 2025 S3. Every wording below, oldest first.

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Question 1
20 Jul 2023 S4
18 $In a certain code language, ‘AROUND’ is coded as ‘CVUCXP’ and ‘ONLINE’ is coded as ‘QRRQXQ’. How will ‘RUSTIC’ be coded in the same language?$
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Question 2
21 Jul 2023 S1
25 $In a certain code language, 'UPSIDE' is coded as 'NJNEAC' and 'GINGER' is coded as 'ZCICBP'. How will 'BRUNCH' be coded in the same language?$
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Question 3
23 Sep 2024 S2
15 $In a certain code language, ‘BAKE’ is coded as ‘FDMF’ and ‘TURN’ is coded as ‘XXTO’. How will ‘MOCK’ be coded in the given language?$
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Question 4
26 Sep 2025 S3
24 $If FRIEND is coded as HUMJTK, how is CANDLE written in that code?$
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Question 1