Find the Length of the Third Side of the Right $\sqrt{61}=30.5$

Multiple Choice

Find the length of the third side of the right triangle. Where appropriate, give both an exact answer and an approximation to three decimal places.
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A) $\sqrt{61}=30.5$
B) 61
C) $\sqrt{31} \approx 5.568$
D) $\sqrt{61} \approx 7.810$