A spaceship of mass 2.20×106kg is cruising at a speed of 5.80×106m/s when the antimatter reactor fails, blowing the ship into three pieces. One section, having a mass of 5.00×105kg , is blown straight backward with a speed of 1.80×106m/s . A second piece, with mass 8.40×105kg , continues forward at 1.20×106m/s .
What is the speed of the third piece?