Question

if sun rises at 4 o'clock in Arunachal Pradesh when it will rise in Gujarat and how Calculate mathematically

Answer 1

If sun rises at 4 o'clock in Arunachal Pradesh ,then if will rise at 6 o'clock in Gujarat because India has a longitudinal extent of 30° longitudes ,
there are 4 minutes in 1° longitude this there is a time lag of 2 hours (30°*4=120 minutes) .

And thus sun takes 2 hours more to rise in Gujarat since it has risen in Arunachal Pradesh.

Answer 2

The reason for time difference between Gujarat and Arunachal Pradesh is of 2 hours as they both lie on different longitudes. 
longitudes have a difference of 4 minutes between each other so if we calculate all the time differences of the longitudes between Gujarat and Arunachal Pradesh , the difference is about 120 minutes (2 hours).