Answer:
$6 = cost of small box
$8 = cost of large box
Step-by-step explanation:
Let s = cost of small box
   l  = cost of large box
(1) Â Â 12s + 3l = 96 Â Â Â Â Â Â (2) Â Â 6s + 6l = 84
  Multiply by -2           -24s - 6l = -192
                        -18s  = - 108
                           s = $6 = cost of small box
   12(6) + 3l = 96
     72 + 3l = 96
         3l = 24
          l = $8 = cost of large box