Critical path method - Help ?

Helo everyvody.

This is my home task:

Activity / Preceding activities

I need to solve project network diagram. By now i have watched many different youtube tutorials about creating network diagrams. Unfortunately, these "youtube and forum" examples are too simple and my home work is level 99.

Closed circles and dead ends are not allowed:

keelatud.jpg

And this is my best result so far:

3._kodune.png

There are so many opened paths which lead nowhere. Any help would be appreciated.