In an astronomical telescope in normal adjustment, a straight line of length L is drawn on inside part of the objective lens. The eye-piece forms a real image of this line. The length of this image is I. The magnification of the telescope is :

1. $\frac{L}{I}+1$

2. $\frac{L}{I}-1$

3. $\frac{L+1}{I-1}$

4. $\frac{L}{I}$

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 the lenses is :

1. 10 cm, 10 cm

2. 15 cm, 5 cm

3. 18 cm, 2 cm

4. 11 cm, 9 cm