A40.0-$kg$ body is moving in the direction of the positive x axis with a speed of 238 $m/s$ when, owing to an internal explosion, it breaks into three pieces. one part, whose mass is 7.0 $kg$, moves away from the point of explosion with a speed of 356 $m/s$ along the positive y axis. a second fragment, whose mass is 4.5 $kg$, moves away from the point of explosion with a speed of 357 $m/s$ along the negative x axis. what is the speed of the third fragment