Trans - first sketch the problem. You have been given some good stuff to start. Two radials, two DME fixes and 15 minutes (or 1/4 of an hour). First the track. Half way, you will be crossing the 355 radial at 90 degrees, so add the two to get 085. Now the distance. Again, at the halfway point, you will be on the 355 radial, having flown from the 310 radial. You have covered 45 degrees. So Cos 40 (0.7071) x 40 = 28.28 x 2 (you are halfway) = 56.57 nm x 4 ( is was a quarter of an hour) = 226 Kts.