3D array can be considered like a cuboid
see following picture
we have to find address of A[p][q][r]
to reach pth frame we must cross 0 to p-1 frames i.e. p frames and each frame contains $y*z$ elements
= $y*z*p$
now to reach qth element in pth frame we have to cross q rows and each row contains z(total columns) elements
=$z*q$
to reach rth elements we have to cross r elements in (p+1)th row
total elements to cross =$(y*z*p+z*q+r)$
now each element occupies m amount of space
therefore total space occupied by these elements = $m(y*z*p+z*q+r)$
so adress of $A[p][q][r]= base adress + Space Occupied by the Elements Before it.$
=$ &A[0][0][0]+m(y*z*p+z*q+r) $
Option (B)