A girl of mass M stands on the rim of a frictionless merry-go-round of radius R and

Question:

A girl of mass M stands on the rim of a frictionless merry-go-round of radius R and rotational inertia I that is not moving. She throws a rock of mass m horizontally in a direction that is tangent to the outer edge of the merry-go- round. The speed of the rock, relative to the ground, is v. Afterward, what are
(a) The angular speed of the merry-go- round and
(b) The linear speed of the girl?