16. Let $a$ be the fractional part of $\sqrt{3+\sqrt{5}}-\sqrt{3-\sqrt{5}}$, and $b$ be the fractional part of $\sqrt{6+3 \sqrt{3}}-\sqrt{6-3 \sqrt{3}}$, then the value of $\frac{2}{b}-\frac{1}{a}$ is $\qquad$
Answer: $\sqrt{6}-\sqrt{2}+1$