There are 27 transparent boxes as in Figure 1. Each layer contains 9 boxes as in Figure 2. Black marbles are placed inside; the top, front and right views are shown. How many marbles are there?
Editorial box convention: each small box contains at most one marble, centred in that box. A black dot in a view means at least one marble lies on that line of sight; overlapping marbles appear as one dot. The source does not explicitly state the per-box capacity.
