Answer:
2808
Explanation:
Sanna can pack 12 layers of 225 small boxes by aligning the 5 cm dimension with the 75 cm dimension (15 boxes) and the 2 cm dimension with the 30 cm dimension (15 boxes).
That will leave an empty space 2 cm by 75 cm by 30 cm. In that space, Sanna can pack an additional 108 boxes by aligning the 4 cm dimension with the 75 cm dimension (18 boxes) and the 5 cm dimension with the 30 cm dimension (6 boxes).
Altogether, Sanna has packed 12 layers of 225 boxes each and 1 layer of 108 boxes, for a total of ...
12×225 + 108 = 2700 +108 = 2808 . . . small boxes
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The empty space will have a dimension of 2 cm by 3 cm by 30 cm.