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7. From a square of pasteboard, 12 inches on a side, square corners are cut, and the sides are turned up to form a rectangular box. If the squares cut out from the corners had been 1 inch larger on a side, the volume of the box would have been increased 28 cubic inches. What is the size of the square corners cut out? (See the figure on the blackboard.)
HARVARD UNIVERSITY
ELEMENTARY ALGEBRA
Time: One Hour and a Half
Arrange your work neatly and clearly, beginning each question on a separate page.