15.15 More on cell phones Refer to Exercise 15.11. That analysis did not take into account the magnitudes of the differences in reaction times. Show how to do this with the Wilcoxon signed-ranks test, illustrating by using only the four observations shown in the table there.

a. State the hypotheses for the relevant one-sided test.

b. Create the sampling distribution of the sum of ranks for the positive differences.

c. Find the P-value and interpret.