If an INS is loaded with 3 waypoints then assume it will be flying between each of the waypoints on a great circle track.
Ie, it will fly between "A" and "B" on a GC and then alter its heading (if necessary) to fly from "B" to "C".
Assume all waypoints are flown over unless otherwise stated...
This type of question normally asks for the direction and number of degrees the aircraft will turn when it reaches "B", thus it'll usually be a nice simple convergency question.
If this is the case for this one then it'll be:
chLong * sin mean lat.
So, 10 * sin 64 = 8.9879, which is 9 degrees for the purpose of this question.
As the GC heading at "B" will be greater than the RL at "B" and the RL from "B" to "C" is the same as "A" to "B" (090), then the aircraft heading will have to turn left 9 degrees (or 8.9 is a bit more accurate).