Linear Algebra System Basic Proof

Given a system of the form

mx + y = c

nx + y = d

where c, d, m and n are constants:

A. Show that the system will have a unique solution if m does not equal n.

B. If m = n, show the system will only be consistent if c = d.

C. Give a geometric interpretation of parts A and B

I have no idea where to begin with that. I tried using elementary row operations on the augmented matrix, but I couldn't gather anything from it and I fear I may have done it incorrectly.

Any help would be greatly appreciated.