Remainder r on dividing by d: remainder on dividing by a factor of d

The same question, asked 2 times: 26 Jul 2023 S3*, 24 Sep 2024 S2. Every wording below, oldest first.

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Question 1
26 Jul 2023 S3
57 $When a number is divided by 45, the remainder is 21. What will be the remainder when the number is divided by 15?$
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Question 2
24 Sep 2024 S2
53 $On dividing a number by 55, we get 28 as the remainder. On dividing the same number by 11, what is the remainder?$
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