Also coming back to " level altitudes " response to mathematical calculations, that's exactly what my instructor asks my when im doing lessons with my instructor, I understand if the aircraft has 40 liters of fuel in it and it consumes 20 liters an hour you will have approximately two hours flying time before fuel runs out, well im hoping that's correct anyways! its just when my instructor asks me " if we have 36 liters of fuel in the aircraft how long will be be able to fly for until we run out of fuel " that's where i tend to get abit confused and flustered and begin to panic, i find it difficult to work them calculations out in my head. Thats what im worried the most about, and if im already worried about the mathematical calculations it doesn't make me feel much better when my instructor comments about how bad i am at doing simple calculations.