Two equal mass billiard balls collide elastically in 1-d

Question

Two equal mass billiard balls collide elastically in 1-D.

A) What is their relative velocity if they are initially approaching each other with speeds vA and v_B? NOTE: their initial relative velocity , v_R, is given by v_R = v_A - v_B

B) What are their final velocities if v_B is initially zero?

C) What can you conclude about 1-D elastic collisions?