bash-busybox, 172 bytes

Result

AC

Duration

468ms

Code [DL]

read j k l
read a b c
read d e f
read g h i
a=$[a-j];b=$[b-k];c=$[c-l]
d=$[d-j];e=$[e-k];f=$[f-l]
g=$[g-j];h=$[h-k];i=$[i-l]
echo $[(a*e*i+b*f*g+c*d*h-a*h*f-b*i*d-c*g*e)/6]

stdin

94 89 76
90 28 38
07 56 28
42 99 46

stdout

16557

stderr

strace