Plz help

The first-serve percentage of a tennis player in a match is normally distributed with a standard deviation of 4.3%. if a sample of 15 random matches of the player is taken, the mean first-serve percentage is found to be 26.4%. what is the margin of error of the sample mean? a. 0.086% b. 0.533% c. 1.11% d. 2.22%

Acollege student takes out a $7500 loan from a bank. what will the balance of the loan be after one year(assuming the student has not made any payments yet) a. if bank charges 3.8% interest each year ?

Ineed some on this. not sure how to solve.