Answer
(c) it is exactly c.
Work Step by Step
The laser beam is an electromagnetic wave. For the entire spectrum of electromagnetic wave from radio frequency to gamma rays, its speed in vacuum is same given by $c=3.0\times10^{8}m/s$.
Since the value of the speed of light in vacuum is same in all inertial frames, the speed of the laser beam relative to the inertial observer is exactly c irrespective of the direction of laser beam.