Correct Answer: Option B

Explanation

\(mean=\frac{60+5x}{18+x}\\3.5=\frac{60+5x}{18+x}\\\frac{7}{2}=\frac{60+5x}{18+x}\)
7(18+x) = 2(60+5x)
126 + 7x = 120 + 10x
10x - 7x = 126 - 120
3x = 6
x = 2

There is an explanation video available below.

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