The great circle crosses the equator at 114° E

The great circle crosses the equator at 114° E. It will cross the equator at what other longitude?

Given:
          Longitude = 114° E

What is asked:
          Longitude where the great circle passes the equator at the west                       longitude.

Solution:

Step 1. Add 180° to the longitude.
          114° + 180° = 294°

Step 2. Subtract 360° by your answer at step 1.
           360 - 294 = 066°

So the answer is 066° West.

The solution above is, I would say, a proper one in dealing this kind of nautical problem. However, as you can see in the diagram, we can make a shortcut solution. Here's how:

Always subtract 180° by the given longitude.

So, 180° - 114° = 066° West.

Thanks.