His question was not "how do I subnet 192.168.1.10/27". If it were, then yes it is duplicate an answered in the linked thread.
His question was where is the instructor getting that he is borrowing 3 bits:
I didn't really understand why he said he'll be using 3 bits
That question is not directly answered by the linked thread, therefore this is not a duplicate. The other thread is related, and should be linked and referred to as additional reading and context. But not used as a reason to close the thread.
The only reference to borrowing bits in the linked thread does not also include the borrowing of bits from a subnet's default Class a/b/c designation. Again, the linked thread does not answer the question.