`a) \sqrt{36}:\sqrt{4}+\sqrt{121}`
`=\sqrt{6^2}:\sqrt{2^2}+\sqrt{11^2}`
`=6:2+11`
`=3+11`
`=14`
`b) \sqrt{6}+2\sqrt{24}-5\sqrt{54}`
`=\sqrt{6}+2\sqrt{4}.\sqrt{6}-5.\sqrt{9}.\sqrt{6}`
`=\sqrt{6}+4\sqrt{6}-15\sqrt{6}`
`=-10\sqrt{6}`
`c) \sqrt{(\sqrt{5}+3)^2}-\sqrt{5}`
`=|\sqrt{5}+3|-\sqrt{5}`
`=\sqrt{5}+3-\sqrt{5}`
`=3`