3a + b + c = -3 (1)
a + 3b + c = 9 (2)
a + b + 3c = 1 (3)
Subtract (1) from (2) Subtract (1) from (3)
-2a + 2b = 12 -2a + 2c = 4
-a + b = 6 -a + c = 2
b = 6 + a (4) c = 2 + a (5)
Sub (4) and (5) into (2)
a + 3 (6 + a) + (2 + a) = 9
a + 18 + 3a + 2 + a = 9
5a + 20 = 9
5a = -11
a = (-11/5)
b= 6 + (-11/5) = 19/5
c = 2 + ( -11/5) = -1/5
abc = (-11/5) (19/5) (-1/5) = 209 / 125