We can split this up into multiple cases to consider.
One-dollar bills: Set up the dividers to get (7-1)C(2)=6C2=15 ways.
Five-dollar bills Again...use the same method to get (6-1)C2=5C2=10 ways.
Twenty-dollar bills: (5-1)C2=6 ways.
Hundred-dollar bills: Any three nephews can get it, so there are three ways or (4-1)C2=3C2=3 ways.
Thus, the answer is 2700 ways.
We have to place an isosceles triangle, 45-45-90 triangle such that the center of the isosceles triangle is the center of the square. The only way to do this is by rotating the isosceles triangles, such that the side is opposite the 90-degree angle. This is 1/4 of the total square or 1/4*100-25 square units.
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