$8\mathrm{.}2($a$)$ Given the data below for a small pipeline project, based on a PERT analysis what is the expected project duration?

$($b$)$ What is the probability of completing this project in $120$ days?

$\backslash$table$[[,,,t_a,t_b,$Followed by Activity$],[$Activity$,$Description,$0,0,0,2],[1,$Start,$10,10,10,3,4,5$