hello, i need a help with my Ds 412 at sfsu. the chapter covers about project management and i need help resolving this difficult question.

The estimated times and immediate predecessors for the activities in a project at Howard Umrah's retinal scanning company are given in the following table. Assume that the activity times are independent. This exercise contains only parts a,b,c, and d a) Based on the activity time estimates, the expected times and variance for each of the activities are (round your response to two decimal places): b) The expected completion time of the project = weeks (round your response to two decimal places). c) The project variance of completion time = weeks (round your response to two decimal places). d) If the time to complete the project is normally distributed, then the probability that the project will be finished in 21 weeks or less = (enter as a probability and round your response to two decimal places)