the answer is (x+5)⁸
here's the proof
recall that
[tex] \sqrt{x} =x^ \frac{1}{2} [/tex] and
[tex](x^m)^n=x^{mn}[/tex]
therefore
[tex] \sqrt{(x+5)^{16}} =((x+5)^{16})^ \frac{1}{2}=(x+5)^{(16)( \frac{1}{2})}=(x+5)^8 [/tex]
the simplified form is (x+5)⁸