Oliver 175 Q Set ( Please explain Q : 94:

The duration uncertainity - defined as pessimistic minus optimistic estimate - of the first activity is 18 days and the second estimate has uncertainity of 24 days . Applying PERT formula fo rpaths , what is the duration uncertainity of the entire path

a. 21 d

b. 30 d

c. 42 d

d. No statement is possible 

Excellent. Thank You very much.