Any standard time zone extends degrees of latitude to the east and west of the central meridian.

I think the correct number to fill in the blank would be 7.5. Any standard time zone extends 7.5 degrees of latitude to the east and west of the central meridian. Standard time is a local time in a specific region or country when DST or daylight saving time is not being used. It is also called as normal time or winter time. Almost all of the time zones are offset from the UTC or the Coordinated Universal time by a certain number of hours from UTC-12 to UTC+14 and there are some time zones that are offset by about 30 minutes to 45 minutes like for the nepal standard time which is UTC+5:45 and the Newfoundland Standard time which is UTC-3:30.