Friction problem help?

Ken and Kim are skating together on a rink at 3.00m/s Ken keeps asking Kim how much she weighs. Annoyed, Kim pushes away from Ken so that she speeds up to 4.00 m/s and he slows down to 2.25 m/s in the same direction. Friction, in the physical sense, is negligible in this drama. If Ken weights 700N. what dies KIM weigh?