See chapter $4,$ page $102,$ question $5.$ The data for activities of the project is shown below:

Activity

Immediate Predecessor

Time $($weeks$)$

A

$-$

$6$

B

A

$3$

C

A

$7$

D

C

$2$

E

B$,$ D

$4$

F

D

$3$

G

E$,$ F

$7$

What is the minimum number of weeks needed to complete the project?