A project is consist of $5$ activities. The durations and interdependencies of the activities are shown in the following table. What is the slack of activity B$?$

Enter your answer in the box as a whole number. For example, if your answer is $2$ days, enter the number $2$ in the box.

Duration Immediate predecessor

A $10$ days $-$

B $9$ days $-$

C $6$ days $-$

D $2$ days A

E $3$ days B