Let
$$f(x) = \frac{1}{1+\frac{2}{1+\frac 3x}}.$$
There are three real numbers $x$ that are not in the domain of $f(x)$. What is the sum of those three numbers?
Denominators cannot equal zero
so x obviously cannot = 0 in 3/x <=====first one
then 1 + 3/x cannot equal zero....so 'x' cannot = -3 <====second one
then 1 + 2/(1 + 3/x) cannot equal zero....this will happen if x = -1 <====third one
Sum total : 0 + -3 + -1 = -4