\textbf{158-} A string with two fixed ends vibrates with frequencies $f_1 = 160\,\text{Hz}$, $f_p = 160\,\text{Hz}$, and $f_p = 320\,\text{Hz}$. $f_1 - f_p$ is how many hertz?
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(1) $250$ \hspace{1cm} (2) $180$ \hspace{1cm} (3) $160$ \hspace{1cm} (4) $80$
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