need help using excel

...3.21 Coleman Rich Control Devices, Inc., produces custom-built relay devices for auto makers. The most recent project undertaken by Rich requires 14 different activities. Rich's managers would like to determine the total project completion time (in days) and those activities that lie along the critical path. The appropriate data are shown in the following table. a) What is the probability of being done in 53 days? b) What date results in a 99% probability of completion? Px