Resposta:

Olá!

A + B = C

[tex]\left[\begin{array}{ccc}0&1&2\\3&4&5\\\end{array}\right] +\left[\begin{array}{ccc}6&7&8\\9&10&11\\\end{array}\right] = \left[\begin{array}{ccc}c11&c12&c13\\c21&c22&c23\\\end{array}\right][/tex]

Então:

c21 = 3 + 9 = 12

c22 = 4 + 10 = 14

c23 = 5 + 11 = 16

Portanto:

c21 + c22 + c23

= 12 + 14 + 16

= 26 + 16

= 42