Number of amine isomers of C4H11N of a given class

This type of question, asked 2 times: 4 May 2023 S1, 12 May 2024 S1. All 2 questions below, oldest first.

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Question 1
4 May 2023 S1
74 $\text{C}_4\text{H}_{11}\text{N}$
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Question 2
12 May 2024 S1
79 $\text{C}_{4}\text{H}_{11}\text{N}$
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