- ∆ABD is right angled hence area:-




There is only one option containing 6x^2 i.e Option D.
Hence without calculating further
Option D is correct
There should be 6 per number
ex.
1234
1243
1342
1324
1432
1423
So floor that you started is x
go down 8 means -8
end on 16
so
x-8=16
add 8
x=24
started on 24