How many degrees are in each time zone and what is the longitude of Philadelphia?

This is from Chapter 4, Exercise 4-3, #35 of Fundamentals of Technical Mathematics (2nd edition): Longitude is measured 0 degrees (the longitude of London on the Greenwich meridian) traveling west parallel to the equator. There are 24 one-hour time zones. (a) How many degrees are in each time zone? (b) If the sun rises exactly 5 hours later in Philadelphia than in London, what is the longitude of Philadelphia?