What value of n makes the equation true ?

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.

Julius sold five times as many computers as sam sold last year. in total, they sold 78 computers. how many computers did julius sell?

What is always true when two whole numbers are subtracted?