5/4+x=3/4 how do I figure this out

For the equation below, x is the input and y is the output. y = -4x + 3 if the input is -8, then the output is

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%

The square root of 9x plus 7 plus the square rot of 2x equall to 7