Let's sum these two numbers.
3 + 21 = 24 total hours.
In every 12-hour the clock format changes AM to PM or the opposite PM to AM. So we need to divide 12 with the result 24.
There are 2 times 12 number in the 24
If the result is ODD number the time format will change the opposite side. If the result is EVEN number the time format will be the same.
Answer :12pm
What is 21 hours from 3am ? = 12pm.
Add 21 hours to 3am is equal 12pm.