Three children each possess a box containing identical
cubic blocks, the same number of blocks in every box.
the first girl is able, using all her blocks, to make a hollow
square, as indicated by a. the second girl, using all her
blocks, makes a larger square, as b. the third girl makes
a still larger square, as c, but has four blocks left over for
the corners, as shown. each girl used all her blocks at
each stage. what is the smallest number of blocks that
each box could have contained? (the diagram does not
represent actual proportions of the various squares.)