golfscript, 114 bytes

Result

AC

Duration

582ms

Code [DL]

"#{require'matrix';a,*b=$stack[0].to_s.lines.map &:split;p Matrix[*b.map{|x|x.zip(a).map{|e|eval e*?-}}].det/6}";;

stdin

71 89 99
76 57 19
95 98 88
69 07 63

stdout

20253

stderr

strace