The following table represents a plan for a project:

JOB NUMBER PREDECESSOR JOB$($S$)$ TIMES $($DAYS$)$

a m b

$1234$

$21123$

$314512$

$413411$

$52135$

$63123$

$74189$

$85,6246$

$982412$

$107345$

$119,10578$ a$)$what is the expected completion time for the project? b$)$ What is the probability that the project will take more than $30$ days to complete?