the time gap is about 6months, so earth will travel half a revolution around the sun. Mars will travel about a 1/3 of a revolution in 6months, that accounts for the posistion of both. The projected path is just a line from earth to mars
The answer to Mars exact position is an approximation.
Based on the HSC markers report yes the better answers had a 1/3 of the position but as it said an approximation would have meant anywhere before a half would have been accepted and marked as correct.