Question 20
If $a,$ $b,$ $c$ are nonzero real numbers such that $$
\begin{aligned} \frac{a+b-c}{c} &=\frac{a-b+c}{b}\\ &=\frac{-a+b+c}{a}, \end{aligned}
$$ and $$
x=\frac{(a+b)(b+c)(c+a)}{abc},
$$ and $x\lt0,$ then $x$ equals
\begin{aligned} \frac{a+b-c}{c} &=\frac{a-b+c}{b}\\ &=\frac{-a+b+c}{a}, \end{aligned}
$$ and $$
x=\frac{(a+b)(b+c)(c+a)}{abc},
$$ and $x\lt0,$ then $x$ equals