stuck, 163 bytes

Result

WA

Duration

482ms

Code [DL]

ssss["x:map(int,x.split())"mT"x:[x[i/3]-x[3] for i in range(3)]"mTu]u]u]["x:(x[1]*(x[5]*x[6]-x[3]*x[8])+x[2]*(x[3]*x[7]-x[4]*x[6])+x[0]*(x[4]*x[8]-x[5]*x[7]))/6"m]

stdin

50 35 20
26 21 56
01 54 38
06 23 35

stdout

stderr

Traceback (most recent call last):
  File "stuck.py", line 167, in <module>
    main()
  File "stuck.py", line 162, in main
    process(prog, stack=[], t=0, nest=0)
  File "stuck.py", line 55, in process
    stack = plugins[plugin].CMDS[char](stack)
  File "plugins/stuck_base.py", line 80, in map_
    return s + [map(eval('lambda '+la),l)]
  File "<string>", line 1, in <lambda>
IndexError: list index out of range

strace