Answer:
616 cm²
Explanation:
small cube (4 sides) = 8 x 3 x 4 = 96
large cube (4 sides) = 7 x 10 x 4 = 280
top and bottom of large cube = 12 x 10 x 2 = 240
(we would deduct the 3 x 3 area from the top of the large cube and add a 3 x 3 area for the top of the small cube. So that cancels each other out.)
total surface area = 96 + 280 + 240 = 616 cm²