Moment!

Distance between supports is 1m+3m+1m = 5m

take moments about LH support to find the force on the RHS

1*300
+4*500
=2300Nm

2300Nm/5m = 460N

take moments about RH support to find the force on the LHS

1*500
+4*300
=1700Nm

1700Nm/5m = 340N

340N+460N = 800N which is the total weight force to be supported

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OR for speed you could just calculate the force on one of the supports and subtract it from 800N to get the force on the other.

Why did u divide by 5

A law of moment is that Upward force=Downward force so upward force=800N

As there are 2 unknown upward force we have to do it in a different way by taking two different pivots at different times

Lets consider LHS as x and RHS as y

Lets take x as pivot.If something is pivot then the moment is considered 0 as F×d and distance is 0,so force on x is not taken
As x pivot then distance are 1m---300N, 4m---500N and 5m----Y N
Put them on our classic Clock=anticlock and you get y force

Now lets consider y as pivot
Y force is not taken as multiplied by zero
1m---500N,4m---300N and 5m----X N

This is a two step process,to check for correct answer,add the two upward force to see if they equal to downward force

If you consider something as pivot then all distance are perpendicular from pivot
Use imagination to know which force is anti clock and which is clock FROM THE CHOSEN PIVOT