How to do this problem?
Answer: From ○+○=4
Get 2 = 4,
That is, 0 is half of 4,
Get ○=2.
(that is, ○=4/2=2. )
From □-○= 1
And ○=2
□-2= 1
From 3-2= 1
Get □=3。
(i.e. □=2+ 1=3. )
So χ = 2,
□=3.