Your friend shoots a 10 g pool ball at 3 m/s to the right. You shoot a second 20 g pool ball to the left (usually billiard balls are the same mass, but yours has been modified to be double the mass of the other) at 5 m/s to the left. Both balls collide and the 10 g ball moves to the left with a speed of 7.7 m/s. What is the final velocity (right is positive and left is negative) of the 20 g ball?