3.65

A.

&A[i][j] in %rdx

B.

&A[j][i] in %rax

C.

addq $8, %rdx # means A[i][j] -> A[i][j+1]

addq $120, %rax # means A[j][i] -> A[j+1][i], 120 == 8*M

M = 15