$6\mathrm{.}4$ Consider the following network problem where the duration, resource $1,$ and resource

$2$ requirements of each activity are presented at each arrow. Use the ACTIM heuristic

to rank activities. Find the minimum project duration:

$($a$)$ If there are $8$ units for the

first resource and $10$ for

the second resource

$($b$)$ If there are $11$ units for

the first resource and $14$

for the second resource