well thats bugga'd me up
i was always told 2 degrees centigrade drop in temp per 1000 feet - so a drop in temp of 6 degrees = 3000 ft , so I would have got it wrong . However the met office give the ELR (environmental lapse rate ) of on average 6.5 degrees per 1000 metres (3281 feet) which means using their reasoning gives an answer of 3028 ft - nearer answer C - so I am confused