Sorry, you chose the wrong figure. Try thinking about the problem using the figures on this page.

These figures illustrate black spheres on a yellow background. The figure showing the least yellow color has the most background covered, so it contains the most black spheres. The figure showing the least yellow illustrates the most efficient packing.

Another way of looking at the problem is to ask which figure contains the most spheres or parts of spheres. The hexagonal array contains the equivalent of 20 spheres, the square array, 18.

Square Array

Hexagonal Array

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