\textbf{133.} Given $\mathbf{a} = (3, m, 5)$ and $\mathbf{b} = (3-m, 7, \circ)$. For a value of $m$, the two vectors $\mathbf{a}+\mathbf{b}$ and $\mathbf{a}-\mathbf{b}$ are perpendicular to each other. What is the angle between vectors $\mathbf{a}$ and $\mathbf{b}$ in this case?
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(1) $30$ \hfill (2) $45$ \hfill (3) $60$ \hfill (4) $90$
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