`1)``(2\sqrt{45}+\sqrt{80}-\sqrt{125}).\sqrt{5}`
`=(6\sqrt{5}+4\sqrt{5}-5\sqrt{5}).\sqrt{5}`
`=5\sqrt{5}.\sqrt{5}`
`=5.5`
`=25`
`3)``(2/(\sqrt{3}-1)+3/(\sqrt{3}-2)+15/(3-\sqrt{3})). 1/(\sqrt{3}+5)`
`=(2/(\sqrt{3}-1)+3/(\sqrt{3}-2)+15/(\sqrt{3}(\sqrt{3}-1))). 1/(\sqrt{3}+5)`
`=((2+5\sqrt{3})/(\sqrt{3}-1)+3/(\sqrt{3}-2)). 1/(\sqrt{3}+5)`
`=((2+5\sqrt{3})(\sqrt{3}-2)+3(\sqrt{3}-1))/((\sqrt{3}-1)(\sqrt{3}-2)). 1/(\sqrt{3}+5)`
`=(11-8\sqrt{3}+3\sqrt{3}-3)/((\sqrt{3}-1)(\sqrt{3}-2)). 1/(\sqrt{3}+5)`
`=(8-5\sqrt{3})/((\sqrt{3}-1)(\sqrt{3}-2)). 1/(\sqrt{3}+5)`
`=(8-5\sqrt{3})/((\sqrt{3}-1)(\sqrt{3}-2)(\sqrt{3}+5))`
`=(8-5\sqrt{3})/(16-10\sqrt{3})`
`=(8-5\sqrt{3})/(2(8-5\sqrt{3}))`
`=1/2`