The expected activity time in PERT analysis is calculated as a. the simple average of the optimistic, pessimistic, and most likely times b. the weighted average of a, m, and b, with a weighted 4 times as heavily as a and m the sum of the activity variances, divided by six O d. the weighted average of a, m, and b, with m weighted 4 times as heavily as a and b O e. the weighted average of a, m, and b, with b weighted 4 times as heavily as m and b