Question

1. What time at 10°E when it is 4 pm at Greenwich?
2. What time at 15° W when it is 10 am at 15°E?

Answer 1

the time at 10°E will be 1600hrs -(10*4)mins.
                                   =1600hrs-40 mins 
                                   =1520 hrs ie.3:20 pm

the time at 15°W will be 1000hr+(30*4)mins
                                   =1000hr+120 mins
                                   =1200 hrs ie 12 noon 

PS.1°=4 mins.