Question 116140
This is how I interpret what the problem is asking you to find.
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When empty, the tank can hold a maximum of 6 cubic feet of water. You find that volume by 
multiplying the three dimensions of the tank ... 1 ft times 2 ft times 3 ft = 6 cu ft.
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When the tank is empty you put the metal cube in it. The question then is how many cubic feet
of water can you then put into the tank before the tank is full. 
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Since the metal cube is 6 inches on a side, each side is {{{1/2}}} foot long. Therefore, the volume
of this cube is the product of {{{(1/2)*(1/2)*(1/2) = 1/8}}} or 1/8 cubic ft
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Once the cube is in the tank, water cannot occupy that 1/8 cubic ft of space. So the amount
of remaining space that water can occupy is the original 6 cubic feet less 1/8 cubic ft
which is 5 7/8 cubic feet or in decimal form 5.875 cubic feet.
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Hope this helps you to understand the problem and how you can work it.
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