The light shifting towards shorter or longer wavelengths as objects in space (stars or galaxies) move closer or farther away from us. This phenomenon is known as the Redshifts and Blueshifts. The concept indicates us that the Universe is expanding.
To find out time, you put distance over speed. So you would have to put 150 over 50. You divide 150 by 50 and you would get 3. So your answer is 3 hours.
