Question

What is the time at point y 30 degrees west when the time at point z is 20 degrees east is 4:0pm

Answer 1

360/ 24 = 15 degrees/hour earlier west than east
so y is 50 degrees * 1 hr/15 degrees = 3 1/3 hours earlier than z
1/3 hr = 20 min
4 pm = 3 pm + 60 min
- 3 hr 20 min
= noon + 40 min
= 12:40 pm

Answer 2

Of course I do navigation, not time zones .