php, 228 bytes

Result

WA

Duration

501ms

Code [DL]

<?php[$a,$b,$c,$d,$e,$f,$g,$h,$i,$j,$k,$l]=explode(" ",readline()." ".readline()." ".readline()." ".readline()),$g-=$a,$h-=$b,$i-=$c,$j-=$a,$k-=$b,$l-=$c,echo(($e-$b)*($i*$j-$g*$l)+($f-$c)*($g*$k-$h*$j)+($d-$a)*($h*$l-$i*$k))/6;

stdin

85 45 36
41 37 28
22 77 31
09 93 07

stdout

<?php[$a,$b,$c,$d,$e,$f,$g,$h,$i,$j,$k,$l]=explode(" ",readline()." ".readline()." ".readline()." ".readline()),$g-=$a,$h-=$b,$i-=$c,$j-=$a,$k-=$b,$l-=$c,echo(($e-$b)*($i*$j-$g*$l)+($f-$c)*($g*$k-$h*$j)+($d-$a)*($h*$l-$i*$k))/6;

stderr

strace