A rocket is launched to space.
The height of the rocket above the surface n minutes after it is launched is h,, kilometres.
The height of the rocket (n + 1) minutes after it is launched, h+, kilometres, is given by
hn+ Kxh+8 where K is a constant.
The rocket is launched from the ground (0 km).
After 2 minutes the rocket reaches a height of 20.4 km.
Work out the average speed of the rocket during the first 4 minutes of the journey.
Give your answer in km/h.