A $1.0$ m ruler lies perpendicular to a plane mirror, with its $100$ cm mark nearest the mirror. The $100$ cm mark is $20$ cm in front of the mirror. Determine the distance between the real $30$ cm mark and the image of the $70$ cm mark.

• A. $160$ cm
• B. $140$ cm
• C. $100$ cm
• D. $120$ cm

Answer: (B)