Calculating Hollow Square Size for a Simple Lifting Machine

[sekedarimaji]

Homework Statement

I'am trying to make a simple machine which is to lift a display up and down. The construction mostly using hollow square.
so far I got the weight of the display and the support is 25 Kg and I have this kind of construction.

if simplified become like this

Homework Equations

which is the right moment happen in that construction?
a.

b.

Is that necessary to calculate the moment?
how do i get the right hollow square size?

The Attempt at a Solution

 

[mfb]

Assuming your frame is rigid, both diagrams are equivalent.

 

[sekedarimaji]

Assuming your frame is rigid, both diagrams are equivalent.

so calculating the moment is not necessary?
is there any formula to get the right size of hollow square?

 

[mfb]

Which moment, necessary for what?
Right size for what?

 

[CWatters]

Ask yourself what forces each tube is subject to. Perhaps start with the horizontal tube.