A solid sphere, a hollow sphere, and a disc, all possessing...

Since the incline is smooth, there is no frictional force to provide the necessary torque for rolling.

Therefore, all the objects will purely slide down the incline without rolling.

The acceleration of any object sliding down a smooth incline of angle $\theta$ is given by $a = g \sin \theta$, which is independent of the mass, radius, and shape (moment of inertia) of the body.

Since all objects start from rest, cover the same distance $s$, and have the same acceleration, the time taken $t = \sqrt{\dfrac{2s}{g \sin \theta}}$ will be the same for all of them.