Problem 7
Time is always an independent variable because time marches on doing its own thing without depending on external forces, or other people/things. Instead, other variables depend on time. In this case, the distance d depends on the independent variable t for time.
If the time goes up by 1 hour, then the distance variable goes up by 3 miles. In short, that tells us his speed is 3 mph.
Answer: Choice A) independent = time; dependent = distance
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Problem 8
Everywhere you see an x, replace it with 9. Then use PEMDAS to simplify
f(x) = 5x - 9
f(9) = 5(9) - 9 ... x replaced with 9
f(9) = 45 - 9
f(9) = 36
Answer: 36