Answer: -70.3 feet
Explanation:
Let Ben's final elevation be represented by x.
We are informed that he starts off 59.3feet above sea level and descends into the canyon and that the difference between his starting and ending elevation is 129.6 feet. This will then be expressed in an equation as:
59.3 - x = 129.6
x = 59.3 - 129.6
x = -70.3
Therefore, the final elevation is -70.3 feet.