The moment of inertia of the topmost object is 28.13 kg·m².
The moment of inertia of the topmost object can be calculated by considering it as a point mass at a certain distance from the axis of rotation. In this case, the topmost object is considered the child, with a mass of 18.0 kg and a distance of 1.25 m from the axis. The moment of inertia (Ic) of the child can be calculated using the formula Ic = MR², where M is the mass of the child and R is the distance from the axis. Substituting the values, we get Ic = (18.0 kg)(1.25 m)² = 28.13 kg·m².