Find the Length of the Third Side of the Right $c$

Multiple Choice

Find the length of the third side of the right triangle. Assume that $c$ represents the length of the hypotenuse. Give an exact answer and, if appropriate, an approximation to three decimal places.
- $\mathrm{a}=1, \mathrm{c}=16$

A) $b=\sqrt{257} ; b \approx 16.031$
B) $b=\sqrt{15} ; b \approx 3.873$
C) $b=15$
D) $b=\sqrt{255} ; b \approx 15.969$