If its 6 PM now so what will be the time after 23990 hours?

A day is of 24 hours.
So if we add 24 hours to 6 PM we will again come back to 6 PM.

now 24 x 1000 = 24000 hours.
So after 24000 hours it will be again 6 PM.

We have been asked to calculate time after 23990 hours, which 10 hours less to 24000 hours.
so lets subtract 10 hours from 6 PM.
It will be 8 AM.

So the answer will be 8 AM.