The expression that shows how much farther Adam can see to the horizon should be considered as the d = 400 - 256 and d = 256 - 400.
Since
Pam's eye–level height is 256 feet above sea level and Adam's eye–level height is 400 feet above sea level.
So here the expression be like The expression that shows how much farther Adam can see to the horizon should be considered as the d = 400 - 256 and d = 256 - 400.
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