In an elastic collision, a rigid sphere moving with velocity v1 collided head-on with another sphere of equal mass moving toward it, as s

In an elastic collision, a rigid sphere moving with velocity v1 collided head-on with another sphere of equal mass moving toward it, as shown in the picture. The second sphere had a velocity 2v1. What was the change in velocity of the first sphere after the collision?
A) v1, moving from left to right
B) v1, moving from right to left
C) 2v1, moving from left to right
D) 2v1, moving from right to left