I need help with this math problem

What is the value of the expression below? (81^2)^1/8

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%

X+y=-4 x-y=2 use elimination with adding and subtraction