If the time is 10.00am in Belfast(longitude 600W), the time at Leningrad(longitude 300E) will be

Longitude is the measure of distance east or west of the prime meridian (0 degrees longitude). Each 15-degree interval of longitude represents a time difference of one hour. Belfast is located at longitude 6°W, which is 6 x 15 = 90 minutes (1.5 hours) behind Greenwich Mean Time (GMT). Therefore, when it is 10.00am in Belfast, it is actually 10.00am - 1.5 hours = 8.30am GMT. Leningrad is located at longitude 30°E, which is 30 x 15 = 450 minutes (7.5 hours) ahead of GMT. Therefore, when it is 8.30am GMT, it is actually 8.30am + 7.5 hours = 4.00pm in Leningrad. So the answer is 4.00 pm.