Let's assume a right-ward motion off the cliff, so that the wheel is rotating in a clockwise fashion. The center of the wheel will obey the equations

This constitutes the answer to a). For the first part of b), solve the y equation for t, when y = R.

The point P will just continue to rotate about the center with constant angular velocity Hence, the vector describing the position of point P is given by

For the second part of b), plug in the time found into this equation to find the position of point P. From that you should be able to figure out, by rotations, which part of the wheel hits the ground first.

c) and d) are plug-and-chug using the standard formulas.

Make sense?