Why do they pick (x - 2)? (Moments and centre of mass)

Simply because they've chosen x to be the distance from A (even though the question doesnt actually ask for that). Id agree that defining x to be the distance from the pivot would be the obvious thing to do and if necessary add 2 at the end to get the distance from A.

Is there a different way I can do it as I would naturally pick to go from the pivot. Do I always go from A in these situations?

As I said in the previous post, Id have picked to take moments about the pivot as well and x would be defined to be the distance from the pivot. There is no good reason to define x as the distance from A in this question.

I'm lost as I've tried doing this and got a different answer.

I've let x to be the distance from the pivot to Sam and got the following when taking moments about M.

35gx = (25g x 0.2) + (25g x 2)

35gx = 539

x = 1.57....

Is there something incorrect with my working?

Try adding 2 to that?

You always have to remember where you start a measurement at. Note the question does not ask for the distance from A, you could answer the question and say its 1.57 m to the right of the pivot.

haha thanks so much for the help. I've been staring at my answer for ages thinking why can I not just use x from the pivot.

I think its time for a break as feel stupid missing that part.

Thanks again