ruby0.49, 340 bytes

Result

WA

Duration

479ms

Code [DL]

freq = {}
x=[]
i=0
while gets()
    for word in $_.split('/\s/')
a=word.split(" ")
    end
x[i]=a 
i=i+1
end
a=x[1][0] - x[0][0]
b=x[1][1] - x[0][1]
c=x[1][2] - x[0][2]
d=x[2][0] - x[0][0]
e=x[2][1] - x[0][1]
f=x[2][2] - x[0][2]
g=x[3][0] - x[0][0]
h=x[3][1] - x[0][1]
i=x[3][2] - x[0][2]
print ((a*e*i+b*f*g+c*d*h-a*f*h-b*d*i-c*e*g)/6)
   

stdin

84 15 39
41 14 07
42 78 66
36 75 07

stdout

stderr

/volume/CODE:11: undefined method `(null)' for "41"(String)

strace