First of all, velocity is a relative phenomenon. When we say velocity of an object is s m/s, it is relative to some other object or a frame of reference (fixed to an object). 1)According to the Theory of relativity, the speed of light is always equal to 3*10^8 m/s. But this velocity is considered relative to what? 2) When two photons are moving in opposite directions, what is the velocity of one photon with respect to the other?