The magnifying power of a telescope is 9. When it is adjusted

The magnifying power of a telescope is 9. When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of lenses are :

M.P. = 9 =	ƒ₀
	ƒ_e

⇒ƒ₀ = 9ƒ_e...(1)
ƒ₀ + ƒ_e = 20...(2)
on solving
ƒ₀ = 18 cm = focal length of the objective
ƒ_e = 2 cm = focal length of the eyepiece