Suppose a new comet, far beyond the planets of our Solar System, is discovered to be 210 billion kilometers...?

Hi. First question, 300,000 km per second so just divide 210,000,000,000 by 300,000, or 700,000 for the time in seconds. Earth is about 4.5 or so billion years old. 4,500,000,000 divided by 200,000. So 1/22,500 of the Earth's age. Or 4.44444444 � 10^-5. Looks like D to me!