Goal: get the ? box all by itself.
Take the same number of blocks off both sides to keep it fair.
? + 3 = 5
Balanced
=
?
1
1
1
1
1
1
1
1
1
Drag a 1 on

The ? box has a mystery weight; every plain block weighs 1. Drag a block off a side to remove it, or drag one from the bottom onto a side. Keep the beam level — whatever you do to one side, do to the other. Get the ? alone and the blocks left on the other side tell you what it weighs.