Answer :
If you consider that the power is the same before and after, you have Pplayer1=81*6,5=Pplayer2=140*SpeedAfter
=> SpeedAfter = 81 * 6,5 / 140 = 3,76 m/s
=> SpeedAfter = 81 * 6,5 / 140 = 3,76 m/s