(a) Difference in time between London 08 hours GMT and Addis Ababa 12.00 noon = 4 hours. The earth rotate through 1° in 4 minutes or through 15° in 1 hour. The difference in longitude = 4hrs x 15° = 60° From the question, time in Addis Ababa is ahead of GMT. Therefore, Addis Ababa is East of the Greenwich Meridian (GMT) located on longitude 60°E.
(b)(i) TIME ZONES:- The world is splitted into 24 time zones. Each cover 15° of longitude. The difference between 2 successive zones is one hour. All places located on the same time zone have the same time. For every 15° movement across the longitude West of the GMT an hour is always lost while to the east an hour is gained.
(ii) STANDARD TIME:- Is the generally adopted time from the central meridian of a Time Zone. It is often set to avoid confusion in local time between one town and the other in the same country. Standard Time spans with 15° of longitude. GMT is a standard time for all the world time zones.
(iii) INTERNATIONAL DATE LINE:- It is longitude 180° East and West of the Greenwich meridian. It is zigzag in structure to avoid cutting across islands. Date changes by one day when crossed east or west. Crossing to the east, gain a day while crossing to the West, a day is lost.