If these are on two separate sketches I don't think you can excepting the following:
- edit the second sketch and use project to reference some of the first sketch geometry i.e. the box. Then using the dimension tool you will be able to specify an offset
- you could redefine the plane of the second sketch by using right click on the sketch in the timeline. This would require the creation of another plane though in the location you require prior to redefining so that you can reference off of it. Easy to do if you jump around in the timeline and create some solid objects which you can then hide/ignore as the basis for your sketch planes.
If it is in the ones single sketch then:
- the dimension you have shown between the two boxes will work so long as everything contained within the boxes is referenced and fully constrained appropriately. It looked like most of your lines were black so this should be right.
- If they are (somewhat) identical sketches albeit flipped you could edit the first sketch and use the mirror function from an arbitrary mirror point i.e. sketch line below at half the distance overall required. You can then select all of the lines and right click break link if you want to then make some edits or leave it constrained if they are identical.
There are probably another few ways to achieve this as Fusion is somewhat flexible when you take into account the timeline and tools at your disposal.
Regards,
David