I need explanation solving this question. id ont understand formula 1 ..= t= (a+m+b)/? we divide by what? Question is below pl help me with formulas and explanation.

Q3. Consider the network described in the table below.

Activity Immediate PREDECESSOR Pessimistic. Probable. Optimistic

J -- 15 10 8

K -- 9 8 7

L J 10 6 5

M J 3 3 3

N K, M 9 5 1

O K, M 10 7 4

P L , N 10 8 3

Draw the network diagram and answer the following questions.

(a) Calculate the expected duration of each activity.

(b) Calculate the expected duration and variance of the critical path.

(c) Calculate the probability that the project will be completed in more than 28 time units.