ruby, 108 bytes

Result

AC

Duration

511ms

Code [DL]

require'matrix'
a,b,c,d=STDIN.read.lines.map{|l|Vector[*l.split.map{|i|i.to_i}]}
p Matrix[b-a,c-a,d-a].det/6

stdin

14 68 69
31 23 04
11 89 39
79 49 86

stdout

27809

stderr

strace