## 1-1-1 distribution of zeros

The function $f(x)= x^{2}(x+2)$ has a 1-2 distribution of zeros while the function $g(x) = x^{2}(x+2)$ has a 2-1 distribution of zeros. For what values of "a" will $f(x) = x^{2}(x+2) +a$ have a 1-1-1 distribution of zeros? For what values of "b" will $g(x)= x^{2}(x+2) - b$ have a 1-1-1 distribution of zeros?

I'm not understanding this? any knowledge about distribution of zeros would be helpful.