csharp, 302 bytes

Result

WA

Duration

830ms

Code [DL]

using System;using System.Linq;class A{static void Main(){char[]c={' ','\n'};string s=Console.In.ReadToEnd();int[]a=s.Split(c).Take(12).Select(Int32.Parse).ToArray();for(int z=8;z-->0;)a[z]-=a[9+z%3];Console.Write((a[7]*(a[0]*a[5]-a[3]*a[2])+a[6]*(a[4]*a[2]-a[1]*a[5])+a[8]*(a[3]*a[1]-a[0]*a[4]))/6);}}

stdin

08 56 05
08 03 68
77 26 74
43 76 34

stdout

11346

stderr

strace