System

a * b * c = -2660/27

My shot: 

$2a+2b+2c=b$

$a+b+c=\frac{b}{2}$

$-\frac{b}{2}=-5+b$

$-5=-\frac{3b}{2}$

$-10=3b$

$b=-\frac{10}{3}$

$a=\frac{34}{3}$

$c=-\frac{59}{3}$

$a\times b\times c=\frac{20060}{9}$

huh, straight we got different answers......