Formula for calculating the GMT zone?

Question

Mathematics

We know that in GMT zone 4 the time is 12:15
We need to find out the time in GMT zone 0.
I calculate it like this: 12 hours - 4 GMT = 8 hours in GMT 0

And what if:
GMT = 5, time = 03:15
We need 3 hours - 5 GMT but we get -2
This time can't be. Please help me write a formula that will calculate the correct hours

Answer 1

-2 hours is 24-2=22 hours