Answer to Question #160859 in Physical geography for ruby

Question

local time is 3 am and the longitude is 120 east what time is the prime meridian

Answer 1

1 hour difference corresponds to 15° difference in longitude. Thus, 120° correspond to

$$t=\frac{120}{15}=8\text{ h}.$$

The longitude is 120° to the east from the Prime meridian, which means that 3 am at 120° is 8 h ahead of the time at the Prime meridian:

$$t_\text{P.M.}=24-(8-3)=19\text{ h},$$

or 7 pm.