The thing is, it's actually two questions in one. It requires you to understand the quadrantal rule and it requires you to understand the difference between flight levels and altitudes, and the function and lower/upper limit of the transition layer.
The highest "altitude" you can fly is 3000 feet on the local QNH, because 3000 feet is defined as the transition altitude (in the UK, outside controlled airspace). You then punch through the transition layer where you reset your altimeter to 1013, and the first FL you hit (multiples of 500 feet) is the lowest FL you can fly.
3000 feet on the 994 QNH is equal to 3000 + (1013-994)*30 feet = 3570 feet on 1013. That means that FL35, in this particular scenario, would be (70 feet) *below* 3000 feet altitude. Because of this, FL35 is not available today. Due to the low QNH. The first usable FL is 40. And FL 40, because of the same calculation, is only 430 feet higher than 3000 feet on the QNH.
So there's no way, with a QNH of 994, that you can do all things right and have the altimeter display 3500. You either fly below the transition layer, in which case you fly at 3000 feet or below on the 994 QHN, or you fly above it, at FL40 or above (with 1013 set).
So on this particular day, if you want to fly to the quadrantal rule, and fly a magnetic track of 139, you've got to fly at either 1500 on the 994 QHN, or at FL55 (5500 on 1013).
(All this of course assumes you want to fly to the quadrantal rule, so this implies that you are flying with the proper QNH set below the transition layer, or with 1013 set above the transition layer. But that's not a requirement for VFR flight so outside this question you've got a lot more flexibility.)
Last edited by BackPacker; 7th March 2011 at 21:04.