Crazy Voyager, thanks for your help, I appreciate it.
marco888: I understand the solution you set out, but since the time they take is the same, then the speed can not be 180 in both cases (as the distances they travel are different), and you've used the same speed for both planes.
So, either the time is the same (which is the case) or the speed, but both, I just don't get it. Sorry.
EDIT: Yeah, it needed a second reading. I get now. Thank-you to to marco888 and Crazy Voyager.