A 45.0 kg girl is standing on a 132 kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. The girl begins to walk along the plank at a constant velocity of 1.37 m/s relative to the plank.(a) What is her velocity relative to the ice surface? (b) What is the velocity of the plank relative to the ice surface?