`a)` `frac{\sqrt{15}-2\sqrt{3}}{2-\sqrt{5}}+6\sqrt{1/3}+frac{13}{\sqrt{3}-4}`
`=frac{\sqrt{3}(\sqrt{5}-2)}{2-\sqrt{5}}+2\sqrt{3}-4-\sqrt{3}`
`=-\sqrt{3}+2\sqrt{3}-4-\sqrt{3}`
`=-4`
`b)` `\sqrt{(\sqrt{7}-3)^2}+\sqrt{11+4\sqrt{7}}`
`=|\sqrt{7}-3|+\sqrt{11+2\sqrt{28}}`
`=(3-\sqrt{7})+\sqrt{4+2\sqrt{4.7}+7}` (do `\sqrt{7}-3<0)`
`=3-\sqrt{7}+\sqrt{(2+\sqrt{7})^2}`
`=3-\sqrt{7}+|2+\sqrt{7}|`
`=3-\sqrt{7}+2+\sqrt{7}` (do `2+\sqrt{7}>0)`
`=5
