DAY 77

Comment

7 is not a factor of 60, so it won't ring at exactly 3 pm.
7 is not a factor of 120, so it won't ring at exactly 4 pm.
7 is not a factor of 180, so it won't ring at exactly 5 pm ...

Answer

It rings at exactly 9 pm.

Readers' methods

XxxxX, Xxxxx XX5:
Xxxxxxxx xxxxxx.

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