Why is 3/12 a rational number

According to modern science, earth is about 4.5 billion years old and written human history extends back about 10,000 years. suppose the entire history of earth is represented with a 10-meter-long timeline, with the birth of earth on one end and today at the other end.

The graph shown is the graph of which function?

If private savings 'v' = 0.75s and total savings 's' equals $4.20 billion, solve for public and private savings.