kotlin, 240 bytes

Result

WA

Duration

5383ms

Code [DL]

fun main(args:Array<String>){
val a=(0..3).flatMap{_->readLine()!!.split(" ").map{a->a.toInt()}}.toMutableList()
for(z in 0 to 8)a[z]-=a[9+z%3]
println(-(a[7]*(a[3]*a[2]-a[0]*a[5])+a[6]*(a[1]*a[5]-a[4]*a[2])+a[8]*(a[0]*a[4]-a[3]*a[1]))/6)
}

stdin

11 16 20
02 35 01
31 88 82
95 15 54

stdout

stderr

/tmp/code.kt:3:10: error: for-loop range must have an 'iterator()' method
for(z in 0 to 8)a[z]-=a[9+z%3]
         ^
Error: Unable to access jarfile code.jar
rm: can't remove '/tmp/code.jar': No such file or directory

strace