A science instructor holds her phone 2.0 m away from a whiteboard. The teacher wants to magnify the device's screen three times using a lens. Determine the focal length and distance at which the lens should be positioned (with respect to the phone) to obtain this effect.

• A. The lens should be 50 cm from the phone and have a focal length of 38 cm.
• B. The lens should be 50 cm from the phone and have a focal length of 72 cm.
• C. The lens should be 100 cm from the phone and have a focal length of 38 cm.
• D. The lens should be 100 cm from the phone and have a focal length of 72 cm.

Answer: (A)