\textbf{136-} The center of a circle is on the first-quadrant angle bisector. If this circle passes through point $A(6,3)$ and is tangent to the line $y = 2x$, what is its radius?
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(1) $\sqrt{5}$ \hfill (2) $\sqrt{6}$ \hfill (3) $2\sqrt{2}$ \hfill (4) $\sqrt{10}$
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