Please solve the bottom highlighted portion and explain:

A7-3 (Algo) The expected times and variances... The expected times and variances for the project activities follow. Complete the table showing which activities are critical. What is the probability of completing the project in 28 periods? Hint: Use the =NORM.S.DIST(z, TRUE) function in Excel to compute the probability. (Do not round intermediate calculations. Round the final answer to 3 decimal places, i.e., 0.750.)