What is the estimated standard deviation in the time for activity Z$?$

Activity

Immediate Predecessor

Optimistic Time

Estimates $($days$)$

Most Likely Time

Estimates $($days$)$

Pessimistic Time

Estimates $($days$)$

U

$\_$

$35$

$50$

$65$

V

$\_$

$28$

$40$

$52$

W

U$,$ V

$26$

$35$

$44$

X

V

$28$

$40$

$52$

Y

X

$26$

$29$

$38$

Z

W$,$ Y

$36$

$60$

$84$

$5$ days

$8$ days

$3$ days

$4$ days

$2$ days