A girl of mass mG is standing on a plank of mass mP. Both are initially at rest on a frozen lake that constitutes a frictionless, flat surface. The girl begins to walk next to the plank at a constant velocity vGP to the right relative to the plank. (The subscript GP denotes the girl relative to the plank.)

(a) What is velocity vPI of the plank relative to the surface of the ice? (Utilize following as necessary: vGP, mG, and mP. Indicate the direction with the sign of your answer. Let positive direction be in the direction that the girl walks.)

(b) What is girl's velocity vGI relative to the ice surface? (Use following as required: vGP, mG, and mP. Indicate the direction with sign of your answer. Let positive direction be in a direction that the girl walks.)