Keep it simple.
The idea of the test is speed and accuracy, aircraft A has 3/4 of an hour head start at 170, so 170x 3/4=127.5
The time for B to catch up is this distance divided by the difference in speeds. 127.5/60=2.125 hours.
The rest should be easy,Ouesburns total distances are wrong though.
They are trying to see if you can work things out quickly, imagine if you were in the air trying to do it the long way, there isn't time.
By the way i'm an old ghit (yes,42!) and i passed OAT last year and i only have 7 O levels and an HNC, no degree. I also worried about the test's, did some revision using some gcse books and passed physics and maths with 100%.
All the best.