The answer would be C - 6 miles. Hope this helps!
They are essentially asking us to solve:

Solving this equation for x tells us that it will take around 80.1 years for the materials in the vault to reduce to 357 pounds.
Answer:

Step-by-step explanation:
An arithmetic sequence that is described by the explicit formula ...

can also be described by the recursive formula ...

Matching parts of the formulas, we see that a1 = 4, d = -7. Putting these values into the explicit formula gives ...

Answer:

Step-by-step explanation:
Given
See attachment for graph
Required
The line graph
First, consider the following points on the graph.


First, calculate the slope.



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Since, the slope is undefined; we simply consider only the value of x.
The line equation is:
