Help with solving X+3/2+2x/7=7

Write a story that matches with the expression 42x-5 pls hurry

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%

We just started the introduction into circles and i have no idea how to do this.