"Ball A with mass 4kg is moving with a velocity of 8m/s North when it crashes into Ball B with unknown mass moving with a velocity of 6 m/s West. This collision is perfectly elastic. If Ball A ends up moving with a velocity of 6.5 m/s @ 120 degrees after the collision, find the final mass and final speed of Ball B if it moves at an angle of 160 degrees after the collision." The formula to calculate an elastic collision is m1v1 + m2v2 = m1v1' + m2v2', where v1' and v2' represent velocities after the collision, m1 and 2 meaning masses and v1 and 2 meaning velocity before collision. I know what I have to do, but I have no idea how to rearrange the equation to solve for both m2 and v2'. Could you guys help me with solving this? I'd really appreciate it.