To determine which situation results in a change that could be modeled by a positive number, we need to find the change in elevation in each case.
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A change in elevation from 632 feet to 312 feet: Change = 312 - 632 = -320 feet (negative change)
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A change in elevation from –12 feet to 123 feet: Change = 123 - (-12) = 123 + 12 = 135 feet (positive change)
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A change in elevation from sea level (0 feet) to -87 feet: Change = -87 - 0 = -87 feet (negative change)
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A change in elevation from 492 feet to -783 feet: Change = -783 - 492 = -1275 feet (negative change)
The only situation that results in a positive change is the second one:
A change in elevation from –12 feet to 123 feet.