I just need an explanation on why I was wrong and why the correct answer is correct

Answer:
C The graph of f(x) is stretched vertically.
Step-by-step explanation:
k is the constant and is most likely to be a WHOLE NUMBER, so you would pick this answer choice, so long as it is a vertical stretch. If it told you that k were a FRACTION, then you will have a vertical shrink, where it stretches horizontally.
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