imgur.com/VTrRX

**Answer 1**

The figure shows that the radius of curvatures of the two lens surfaces are each 40 cm.

The focal length is half the radius of curvature.

R = 40 cm

FL = R/2 = 20 cm.

Hope this helps,

-Guru

**Answer 2**

Actually the correct answer is 40 cm. Take those two arrows and slide them along the lens, you’ll see that they both touch at the x-axis.

Source(s): I just did it on MasteringPhysics…