Matrix computation complexity:

A. Two matrices A = [ 11 12 13 21 22 23 31 31 33 ] and B = [ 11 12 13 21 22 23 31 31 33 ].

In order to compute matrix multiplication AB, how many multiplication do you need?

B. Two matrices A, B with equal size (N N), how many multiplication do you need to compute AB. (express in terms of N)