=>Total longitudes = 360
=>Sun ray stay on 1 longitude for 4mins... So 360*4=1440mins
=>One hour is 60mins,so dividing 1440/60 = 24hr.
=>Sun ray on 1 longitude for 4mins
=>So in one hour it crosses 60/4=15 longitudes
==> Countries which are towards east of Greenwich we add the time and countries which are towards west of Greenwich we subtract the time
==> 82.5 is the standard meridian of India
==> 82.5/15=5.5 that is why India is ahead of 5.5 hours from Greenwich