\textbf{156.} The sum of vectors $\vec{A} = 9\hat{i} + 12\hat{j}$ and $\vec{B}$ is a vector in the positive y-direction and has the same magnitude as vector $\vec{A}$. What is the magnitude of $\vec{A} - \vec{B}$?
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(1) $9$ \hfill (2) $9\sqrt{2}$ \hfill (3) $9\sqrt{7}$ \hfill (4) $9\sqrt{5}$
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