Find the modular inverse of $4$, modulo $21$.

Express your answer as an integer from $0$ to $20$, inclusive.
Question:
Find the modular inverse of $4$, modulo $21$.

Express your answer as an integer from $0$ to $20$, inclusive.
Answer:
Let's think step by step.

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16
Find the modular inverse of $4$, modulo $21$.

Express your answer as an integer from $0$ to $20$, inclusive.
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