Let a continuous and equal constant value be k, then a+b-c=kc, …

A+b = (k+ 1) c，c+b = (k+ 1) a，a+c = (k+ 1) b。

Addition and simplification result in (k- 1)(a+b+c)=0. As the title, K- 1 = 0, K = 1.

Then a+b=2c, ...

So the target =(2c×2a×2b)/(abc)=8.

Certification completed