b) Second postulate says that the speed of light in vacuum is a constant (often denoted as $c$) and is the same measured from any inertial reference frame.

There are theories that predict the existence of so called tachions (particles that move faster than light) but according to relativity there is no way of detecting them. For example, the time interval transformed from a inertial frame of reference to a frame tied to tachion would be imaginary and there is no physical meaning in that. Note that this is true only in inertial frames while in non inertial frames we could measure particles moving faster than light.Also light travels slower in continuous medium than in vacuum and it is possible for a massive particle to move faster in that medium than the light does (but not faster than $c$) and this is known as Cherenkov effect.

One of Einstein’s postulates states that: the laws of physics have the same form in all inertial reference frames. Thus, the outcome of an experiment doesn’t depend on the observer. In our case, we see that the achieved result in an experiment is the same for both an observer in a moving car with velocity $100 frac{text{km}}{text{h}}$ as for an observer in a laboratory frame of reference.

Einstein’s 2nd postulate states that the speed of light in vacuum $c$ is the same in all inertial frames of reference. This means that the speed of light does not depend on the observer, thus the stationary observer sees the light approaching her with a speed that is equal to the speed of light.