`a,4\sqrt{20}+5\sqrt{45}-3\sqrt{125}-15\sqrt{1/5}`
`=8\sqrt{5}+15\sqrt{5}-15\sqrt{5}-3\sqrt{5}=5\sqrt{5}`
`b,\sqrt{11-4\sqrt{7}}+\sqrt{16+6\sqrt{7}}`
`=\sqrt{11-2\sqrt{28}}+\sqrt{16+2\sqrt{63}}`
`=\sqrt{7-2\sqrt{28}+4}+\sqrt{9-2\sqrt{63}+7}`
`=\sqrt{(\sqrt{7}-2)^2}+\sqrt{(3-\sqrt{7})^2}`
`=|\sqrt{7}-2|+|3-\sqrt{7}|`
`=\sqrt{7}-2+3-\sqrt{7}=1`
`c,(\sqrt{10}-\sqrt{2})(3+\sqrt{5})\sqrt{3-\sqrt{5}}`
`=\sqrt{2}(\sqrt{5}-1)(3+\sqrt{5})\sqrt{3-\sqrt{5}}`
`=(\sqrt{5}-1)(3+\sqrt{5})\sqrt{6-2\sqrt{5}}`
`=(\sqrt{5}-1)(3+\sqrt{5})\sqrt{5-2\sqrt{5}+1}`
`=(\sqrt{5}-1)(3+\sqrt{5})\sqrt{5-2\sqrt{5}+1}`
`=(\sqrt{5}-1)(3+\sqrt{5})\sqrt{(\sqrt{5}-1)^2}`
`=(\sqrt{5}-1)(3+\sqrt{5})|\sqrt{5}-1|`
`=(\sqrt{5}-1)(3+\sqrt{5})(\sqrt{5}-1)`
`=(\sqrt{5}-1)^2(3+\sqrt{5})`
`=(5-2\sqrt{5}+1)(3+\sqrt{5})`
`=(6-2\sqrt{5})(3+\sqrt{5})`
`=2(3-\sqrt{5})(3+\sqrt{5})`
`=2(9-5)=2.4=8`
