Answer: 6 ft
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Explanation:
The mirror is 4 ft wide and we have 16 ft of wall to work with. That leaves 16-4 = 12 ft of buffer room or empty space. Splitting that empty space into two equal regions (left and right) means 12/2 = 6 ft is the width of the empty space on either side.
Therefore, each end of the mirror should be 6 ft from either end of the wall. Refer to the diagram below. Note how all of the values in the second row add to 16.
