Restitution coefficient

Two balls $$A$$ and $$B$$ with the same mass are pendent from the ceiling. First, ball $$A$$ is raised by $$90$$° to the left and then dropped, so that it collides with ball $$B.$$ Then, ball $$B$$ goes up by $$60$$° to the right. What is the restitution coefficient between the two balls? (Ignore air resistance and the masses of the strings.)

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