Lens-Maker's Formula: a Lens Is Made with a Focal Length

Multiple Choice

Lens-maker's formula: A lens is made with a focal length of -40 cm using a material with index of refraction 1.50. A second lens is made with the SAME GEOMETRY as the first lens, but using a material having refractive index of 2.00. What is the focal length of the second lens?

A) -40 cm
B) -80 cm
C) -53 cm
D) -20 cm
E) -30 cm