The first answer is correct; the following two have missed the fundamental, and non intuitive, aspect of relativity...the speed of light is constant no matter what the source, no matter where the observer is...no matter what. That's the remarkable thing about what Einstein came up with...it's totally at odds with the speed of all other things.

So if you were on a speeding train and tossed a ball forward of the train, the velocity of the ball would be that of the train plus whatever your strong arm could provide. Not so with light. If that train is now going at light speed (if it could) and the ball is now a photon, that photon would still be going at light speed, as (get this because it's important) both you on the train and your worried mum standing on the ground watching you see it. That is, despite the speed of the train, you both see the light traveling at the same speed, i.e., c the speed of light.

How could this be? The simple answer is this...space and time are altered when mass approaches light speed. And those alterations cause both observers, on the train and on the ground, to see light speed as being the same speed.