Can someone tell me if I’m right?

What is the standard deviation of the following data set rounded to the nearest tenth? 3, 17, 18, 15, 12, 21, 9

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?

Jalen charges $25.50 for every 3 hours of yard work he does for his neighbors. ralph charges $34 for every 4 hours of work that he does. who charges less? opinions: 1.they charge the same amount 2.jalen 3.ralph