6. The height, h metres, of a shrub, t years after it was planted, is modelled by the differential equation dh 2hz t > 0 dt 15 +2' (a) Given that after 1 year the shrub's height was exactly 1 metre, show that at 2 h = ( 1 + bt ) 2 where a and b are constants to be found. (b) Hence find, according to the model, the limit of the height of the shrub. (7) (2)