three

Both the external figure and the internal figure are a number. If the external number is greater than the internal number, subtract the internal number from the external number. If the external figure is smaller than the internal figure, the internal figure is added with the external figure. Negative numbers can't appear anyway. The logical conclusion is 3.

Calculation:

Ο=2,□= 1,Δ=5

External □= 1, internal ο = 2, 1+2=3.

External zeta = 2, internal □= 1, 2- 1= 1.

External □= 1, internal δ = 5, 1+5=6.

External δ = 5, internal□ =1,5- 1=4.

therefore

External δ = 5, internal zeta = 2, 5-2=3.