Any Great Circle Track crossing the equator will cross the equator again at the exact opposite side of the earth, i.e. if it crosses at the Greenwich Meridian it will cross again at the Greenwich Ante-Meridian. The longitudes of both crossing points will have opposite signs, i.e. one will be West and the other East and they will add up to 180°.

Therefore, if it crosses at 030°W it will cross again at 180° - 030° = 150° and in the opposite hemisphere = 150°E.

This is a Great Circle Track which is subject to convergency and which starts at 035°T (in a north-EASTERLY direction) where it crosses the equator at 030°W. At 150°E the GCT will have changed from a north-easterly track to a south easterly track over 180° of longitude.

The point where the track is either due East or due West is also the point where the track reaches its highest latitude, which also happens to be at the mid-point, i.e. Change of Longitude to the mid-point = 90°

030°W + 90° (Easterly) = 060°E