Hi I am having difficulty with this question:

Consider a simple “system” of a thin lens with focal length 12 cm, an input
plane at 25 cm in front of the lens and an output plane at 11 cm beyond the lens.

a) Find the matrix for the simple system
b) Why is B = 0 in this case? What is the meaning of A in this case?

Input plane? No idea what that means.