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8. Devin is driving from Salt Lake City, Utah,
to Denver, Colorado. So far he has driven
80% of the distance, or 400 miles. How far is
the distance from Salt Lake City to Denver?

The answer is the option A, which is: A. x-7=x²+2x-4
 The explanation is shown below:
To solve this problem you must apply the proccedure shown below:
 1. You have the following system equations given in the problem above:
 y=x-7
 y=x²+2x-4
2. Therefore, when you substitute for y in the bottom equation, you obtain:
 x-7=x²+2x-4