Answer
$45^\circ.$
Work Step by Step
If $v=ai+bj$ then by definition $tan(\alpha)=\frac{b}{a}$, hence $\alpha=tan^{-1}(\frac{b}{a})$. Also $0^\circ\lt\alpha\lt360^\circ.$
Therefore here $\alpha=tan^{-1}(\frac{3}{3})=tan^{-1}(1)=45^\circ.$
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