Does anyone know how to calculate the below. 

Question:

Together with your team you applied three point estimation on a  Critical path containing two activities.

The following duration uncertainities are calculated using +/-3sigma confidence interval.

The duration uncertaining-defined as Pessimistic minus optimistic estimate - of the first activity is 18 days; the second estimate has an uncertainity of 24 days. Applying the PERT formula for paths, what is the duration uncertaining of the entire path?