A digital lock has a secret code formed by the number $\Theta$. Given the equation $252 / \Theta = \underline{3\Theta} + \Theta$, where $\underline{3\Theta}$ represents a two-digit number with $3$ in the tens digit and $\Theta$ in the ones digit, find the digit $\Theta$. Let's think step by step and output the final answer within \boxed{}.
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