Hi, here you need to balance the moments being supplied by each weight.
So if we define x as the distance from the 600kg weight to the support
Using:
Moment = Force * Perpendicular distance (from fulcrum)
and:
Counterclockwise moment = Clockwise moment
we find:
this describes the moment felt in the clockwise and anticlockwise direction.
600*x is the moment from the weight
20(x/6) is the weight of the bar felt in this direction
x/2 is the distance that the weight of the bar acts from the fulcrum
then the same is written for the other direction
The first step is obviously to cancel g, this is why I put it in brackets.
You can solve this equation for x to find the distance that the fulcrum must be from the 600kg weight
If you have any problem with understanding, please ask further!
good luck!
PS: i did this very quickly and have tried to catch any errors, I make no claims to correctness and you should check everything yourself.