How many years are there between 25BC to 16AD?

The year 1 BC was immediately followed by the year 1 AD. So from the end of 25 BC to the end of 1 BC was 24 years and from the beginning of 1 AD to the beginning of 16 AD was 15 years.

So the number of years between the 25 BC and 16 BC = 24 + 15 = 39 years.