On a piston engine, how do I figure out the torque to a crankshaft when I have the force on a piston, the length of the connecting rod, the length of the crank throw and the crank angle?

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%