Question

What is the longitude of a place where the local time is 1:15pm when it is 4am at Chicago (88.w) why is 6hrs ahead

Answer 1

As the earth rotates from west to east, those places that lie east of Greenwich are ahead than the places that lie to the west of Greenwich.

When it is 4 AM at Chicago (set to 90°W). GMT is (6hrs ahead) 10 AM.

From there 1:15 PM is 3¼ hrs ahead (to east),

3¼ X 15°E

= 48° 45'E.