What are the missing values for 15? 20? 23? How did you get those?

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.

There were 25 students who answered to a survey about sports. four-fifths of them like football. how many students like football?

Math i have no idea how to do a and b