vim, 185 bytes

Result

WA

Duration

524ms

Code [DL]

00000000  56 47 4a 3a 6c 65 74 20  6c 3d 6d 61 70 28 73 70  |VGJ:let l=map(sp|
00000010  6c 69 74 28 67 65 74 6c  69 6e 65 28 31 29 2c 27  |lit(getline(1),'|
00000020  20 27 29 2c 27 73 74 72  32 6e 72 27 29 0a 3a 66  | '),'str2nr').:f|
00000030  6f 72 20 69 20 69 6e 20  72 61 6e 67 65 28 39 29  |or i in range(9)|
00000040  0a 6c 65 74 20 6c 5b 69  2b 33 5d 2d 3d 6c 5b 69  |.let l[i+3]-=l[i|
00000050  25 33 5d 0a 65 6e 64 66  6f 72 0a 43 12 3d 28 6c  |%3].endfor.C.=(l|
00000060  5b 33 5d 2a 28 6c 5b 37  5d 2a 6c 5b 31 31 5d 2d  |[3]*(l[7]*l[11]-|
00000070  6c 5b 38 5d 2a 6c 5b 31  30 5d 29 2b 6c 5b 34 5d  |l[8]*l[10])+l[4]|
00000080  2a 28 6c 5b 39 5d 2a 6c  5b 38 5d 2d 6c 5b 31 31  |*(l[9]*l[8]-l[11|
00000090  5d 2a 6c 5b 36 5d 29 2b  6c 5b 35 5d 2a 28 6c 5b  |]*l[6])+l[5]*(l[|
000000a0  36 5d 2a 6c 5b 31 30 5d  2d 6c 5b 37 5d 2a 6c 5b  |6]*l[10]-l[7]*l[|
000000b0  39 5d 29 29 2f 36 0a 5a  5a                       |9]))/6.ZZ|
000000b9

Disassembly

VGJ:let l=map(split(getline(1),' '),'str2nr')<NL>:for i in range(9)<NL>let l[i+3]-=l[i%3]<NL>endfor<NL>C<C-R>=(l[3]*(l[7]*l[11]-l[8]*l[10])+l[4]*(l[9]*l[8]-l[11]*l[6])+l[5]*(l[6]*l[10]-l[7]*l[9]))/6<NL>ZZ

stdin

17 10 81
03 02 49
09 29 07
56 12 89

stdout

17 10 81
03 02 49
09 29 07
56 12 89

stderr

strace