A playground carousel ("merry-go-round") is free to rotate frictionlessly in the horizontal plane (and air resistance is negligible). Without riders, the carousel has a moment of inertia of 152 kg·m^2. But there is a single rider, initially standing 1.85 m from the axis of rotation, as the carousel turns at an angular speed of 0.640 rad/s. Then the person moves to another location, 0.75 m from the axis, and the angular speed is then 0.973 rad/s. Find the person's mass.