It is important on your software development project to accurately estimate the durations of activities. You suggest to management that PERT estimates be completed on each activity. You give them the following example. Your programmer estimates that most likely it will take $100$ hours to complete the work. Optimistically it may only be $80$ hours and pessimistically it could take as long as $150$ hours. The PERT estimate is:

a$)100$ hours

b$)105$ hours

C$)110$ hours

D$)150$ hours