Please answer and explain how you go the answer

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%

Which of the following is the best first step in solving the equation below? 4+2㏒³x=17

A+b= 17, ab=70, find the value of |a-b|