SUBTRACTING FRACTIONS PLS HELP

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?

You just purchased two coins at a price of $670 each. because one of the coins is more collectible, you believe that its value will increase at a rate of 7.1 percent per year, while you believe the second coin will only increase at 6.5 percent per year. if you are correct, how much more will the first coin be worth in 15 years?