Moments help....

Steeple jack rides on a beam,The mass of the beam and the mass of the steeple jack is 2000kg and 80kg, respectively, the length of the beam is 12m, and chains hang vertically, from the crane, one chain 10m from the left end, and second chain on the very end of the left end. The steeple jack sits at a distance of 7m from the left end. Find the tension in each of the chains. (Beam is horizontal and at rest)

my working:
$-80g(3)-2000g(5)+T1(10)=0$

have i done anything wrong?

Diagram:

yoi should have multiplied the mass times 9.8 to get the weight in newtons

I assume you took the chain to the right as the pivot? In which case, the centre of mass of the beam is 4 away from the the pivot, not 5. I assume the beam is uniform.

it doesnt say it is in uniform.

Then where is it's centre of mass?

They didnt say it was in uniform, but i think we had to assume it was, as using 4 instead of 5, i managed to get the correct answer.

Why is it 4 though? Thats the bit i struggle with.

The length is 12, so COM is halfway there which makes the distance from the right end 6. Distance from COM to right chain = a, so distance from right chain to left end is 2, hence 4+a=6 and so a=4