The following are the results of a Wagner turbidity test performed on 15 samples of a standard Ottawa testing. The values are in microamperes. 26.9, 25.8, 24.4, 24.1, 26.4, 25.9, 24.0, 21.7, 24.9, 25.9, 27.3, 26.7, 26.9, 24.8, 27.3 (a) Find the point estimate of its mean. (b) Calculate the margin of error. (c) Construct a 98% confidence interval for the sample mean